Just been switching to beancount from ynab. Apart from minor annoyances it's so much more powerful. If you're up for some programming and customization it's hard to beat (your choice between beancount/ledger/hledger matters less).
Are you trying to import YNAB's budgeting philosphy into Beancount? If so, how? I've considered the same transition but was unsure how to handle having budgetary categories dissociated from physical accounts.
Actually, not really. I found out I never used the budgeting functionality other than to keep track of my previous spending.
I haven't found an existing tool to budget in beancount so you'd have to write it yourself. Other people have successfully used Ledger's virtual postings (which doesn't exist in beancount) for budgeting though[0]. It might be a way forward for you?
The reason why I disliked GnuCash was the lack of an undo together with a frickly date entry.
I recommend reading up on https://plaintextaccounting.org/ for those who like double entry but with text files