I'm so glad you are going to get to enjoy HOD next year!

Bigger Hearts is the transitional bridge for many skills between Beyond and PHFHG. Bigger Hearts teaches many LA skills in preparation for PHFHG. Writing skills, in particular, change much in amount and in difficulty. Carrie described this so well in a past post, that I will cut and paste the portion that pertains to the writing skills progression from Beyond to PHFHG, so you can see if it would be better for dc to do Bigger Hearts or if they are ready for PHFHG...
In Beyond, we begin daily copywork of poetry and 4 times weekly written spelling word practice. We also practice writing sentences with the spelling words. We add an entry to the timeline almost weekly and do some written work within the gentle grammar lessons once weekly. Oral narration skills and a mini-Drawn into the Heart of Reading in the Storytime Box are practiced daily in Beyond in preparation for the written work that will come in these areas as students progress into Bigger Hearts and Preparing Hearts. Once each genre, students are asked to orally narrate while the parent writes down the narration to keep. We also continue writing in some of our project work and daily in math. Once kiddos begin Drawn into the Heart of Reading, there is also written work within that.
Our focus in LHFHG and Beyond is to allow kiddos to mature and strengthen their fine motor skills a bit at a time, gently build up their spelling and grammar skills, and begin forming the habit of correctly written copywork, before we ask the kiddos to do much formal writing.
In Bigger Hearts, we begin to head into more written work. We have kiddos begin cursive handwriting with the aid of a cursive workbook to practice correct letter formation. We work on 1-3 vocabulary cards each week with words from their history stories. Students use the context of the word to guess its meaning in the story, choose and copy the word's definition in the dictionary, use the word in a sentence, and draw a picture that shows the word's meaning. Students add to a timeline entry each week, and create a history notebook page with guided copywork and sketching from their history stories. They begin daily grammar lessons through Rod and Staff English 2 and should write one small portion on paper each lesson to practice learning to write smaller on wide-lined paper. The last chapter of Rod and Staff English 2 includes some writing lessons, after students have a better grasp of English overall.
In Bigger Hearts, students also copy the Bible verse they memorize each week. In addition they do a science notebook sheet each week with copywork of a Bible verse that matches their science reading. Along with the copywork, they are instructed to sketch and label specific diagrams or illustrations from their science readings. A formal lab sheet with question, guess, procedure, and conclusion is also completed each week, with the question and the steps to the procedure provided in the plans. Experiments match the science readings, giving students some foundation on which to base their guess. Typically, Drawn into the Heart of Reading is begun here too, meaning some writing in that area as well.
In Preparing Hearts, there is daily copywork scheduled to be done in cursive. The copywork rotates by day through history, science, and Bible. Students also do copywork through Draw and Write Through History. Formal written narration instruction begins at this level once weekly. Guiding questions are provided to help students think about what they read before they begin to write. Students begin writing a 3-5 sentence narration and move to writing a 5 sentence narration. As the year progresses, students are asked to highlight or underline the main idea sentence in their narration. Students also begin to keep a Common Place Book, in which they are directed to copy their Bible verses from the week (which they add to as the year progresses because they are memorizing entire Psalms at a time), as well as quotes, and passages from their literature. The students choose a poem to memorize each 9 weeks and this chosen poem is also copied in the Common Place Book.
In Preparing Hearts in science the lab sheet is continued, as well as the copywork and sketching within the notebook, but students also begin answering questions about the readings each week. Vocabulary cards are continued and move up to 3-5 words each week. A timeline is done, in a stairstep fashion or an accordian fashion and added to each week. Rod and Staff English 3 or 4 is used and both levels include formal writing instruction. Studied dictation is underway at this age, training the students in capturing correct spelling in their minds and reproducing it correctly on paper (including punctuation, usage, and grammar too). Students also practice and begin forming the habit of proofreading through comparing their passage to the correctly written one. In Preparing Hearts, we also begin teaching the writing process through once weekly writing lessons that stem from the poetry of Robert Louis Stevenson. Drawn into the Heart of Reading continues to firm up the skills of expressing what was read in written form and in gathering a student's thoughts and getting them down on paper.
Whether students used the Emerging Reader's Set or Drawn into the Heart of Reading in Bigger Hearts, they had daily reading instruction with comprehension questions from each of the levels of Bloom's Taxonomy (which includes harder comprehension questions from they synthesis, analysis, and application levels, rather than just basic comprehension questions). This helps them be ready for many parts of PHFHG in various subject areas. It helps them be able to move on to the next level of DITHOR, but it also helps them be ready for independently reading and completing the science and history boxes of PHFHG. Likewise, the oral narration practice with guidance from the teacher in Storytime (as well as other skills taught) help prepare students for the harder skill or written narrations in PHFHG. Here are the skills taught in Bigger Hearts' Storytime, to help explain this further...
*Day 1: introduce and study different types of literature
*Day 2: model narration to foster comprehension
*Day 3: identify and analyze a different story element for each genre
*Day 4: relate personally to one Godly character trait, compare Biblical and book characters, and make a bookmark as a reminder of the trait
*Day 5: practice narration by retelling the story
The poetry lessons in Bigger Hearts help dc be prepared for the creative writing of poetry in PHFHG as well. If dc are new to poetry study and skills at the start of PHFHG, the creative writing of it is more difficult. Here are the skills taught in BHFHG to prepare dc for the creative writing of poetry in PHFHG...
*Day 1: introduction of the poem and any unfamiliar vocabulary
*Day 2: questions and discussion related to the meaning of the poem
*Day 3: instruction on various ways to choral read the poem
*Day 4: a poetry lesson focusing on poetic devices
*Day 5: reading of past poems for enjoyment
Science is another area that Bigger Hearts prepares dc for nicely. Dc practice the skills alongside a parent in BHFHG, and then take over that box in PHFHG. Here are the skills taught in the BHFHG science box in preparation for students being ready to do this independently in PHFHG...
*Day 1: practice narration by retelling the science story
*Day 2: create a science notebook entry
*Day 3: conduct an experiment related to the reading and log it in a science notebook
*Day 4: practice narration by retelling the science story
*Day 5: conduct an experiment related to the reading and orally discuss it
Bible Study is modeled in BHFHG and in PHFHG, dc take over a portion to begin their own Bible Quiet Time. Vocabulary words increase in difficulty and number. Devotions are deeper. Notebooking assignments are harder with more directions. These are all areas practiced in BHFHG that become more difficult in PHFHG. I am hoping that by describing the bridge of skills between Beyond and PHFHG via Bigger Hearts, you will be able to see which guide dc would be better placed in. I hope something here helps, but they are both absolutely wonderful guides!

I'd pick based on skills, as the content in both is amazing. HTH!
In Christ,
Julie