I'll wait for Bannerlord to be finished before I chose definitively.
I will say warband has many many things I wish were copies into bannerlord.
In fact, I and many players wish it would have been say 90% exactly copied mechanics from warband and the more stuff added later.
1: Power level of tiers of troops. Bannerlord they're too weak. Warband you high tier troops feel really powerful!
2: Cavalry and Infantry: Both are weak and die too much in Bannerlord. Both were very strong in Warband.
3: Being KING. Bannerlord you have no control, only slight advantage in voting. Warband you have some control and final say on fiefs, I like this better.
4:Recruiting Lord: Bannerlord they just want money and they're all the same. Warband, relation matter much more, each personality of lord is different, some are much better vassals and you can creat lords of you companions too!
5: Armor and damage: Bannerlord, best armor you still die in 2 hits. Warband best armor.... you get 3 or 4.... it makes a big difference though.
6: Passive skills: In bannerlord some are fast and some are slow or impossible to skill up. Warband you spend your points, you get your ability levels, it works. I like this because it works, I can make a much more useful character in warband. I like that.
&: Tid bits: Books, Sword sisters, dependable workshops, 1/2 wages for garrisons, ALL good stuff!
There's lots more too, in fact like I said, 90% of warband could just replace it's bannerlord equivalent and probably be a strait improvment.