The Halo Infinite battlepass is probably the best one tbh. Only cosmetics, never expires after you buy it and gives you enough credits to buy the next one once you complete it. Also not a colossal time-sync. 10 ish matches per week will have you finishing it with plenty of time to spare.

Both Destiny and Overwatch put exotics/heroes behind their battlepasses (instantly unlocked for premium, free track has them fairly deep in) but these can be unlocked fairly easily after the season is over. Not ideal but if it means we get content regularly then I don't think it's a big deal.