Depends on the clientele. If you're doing the books, then jumping right on those LLC returns can be a good use of January working hours. If you do more payroll, then the W2s and 941s will take your attention. If you have a bunch of Schedule C folks who send 1099s, that's another time sink. Even if you have lots of college-kid parents who need FAFSA info can grab a bunch of your January.
We used to spend a gazillion hours on FAFSA forms in January, then for some years it was 1099s. Now it's more W2s (the kids grew up, the small businesses expanded to employees instead of temp workers). Examine your own client list and the snafus for the last year or so, and see what it makes most sense to jump on quickly - then warn the right client set that you want to jump!