I have played both BKB and VH's XL mods. I can relate to your preference for the BKB mod, although I gave up on it, due to stability problems (the game would repeatedly crash on my PC for some odd reason). So I'm currently playing the VH mod, which I also like. Some thoughts:

BKB mod:
+ Large number of factions
+ The Asian/Russian factions seems more developed
+ Seems more historically correct, with more details.
- A few odd bugs (for instance, I got attacked in Rum by the English, although I had all surrounding provinces - should be impossible, but alas it happened - and it was not a rebellion)
- Large load times (at least on my rig)
- A total overwrite, cannot play original game (AFAIK)
- Sometimes the vast number of new unit types can be annoying/overwhelming, especially because the real difference between units are limited (there's after all only a few parameters to modify). And you (I) don't want your (my) army to consist of umpteen different unit types, since that makes combining unit fragments more difficult.

XL mod:
+ Reasoneable load times, and more stable (for me)
+ No or few odd bugs (at least I have not met any yet :-) )
+ The revamped economic system not so dependent of trade.
- Asian/Russian factions seems under-developed, only a few special units, of which several only apply to the early era.
+/- Not as huge as BKB in terms of factions and units, but it also IMO makes for a more balanced and focused game.

I can understand why some call XL mod a "BKB Lite" mod, although I regard XL as a fine piece of work in its own right. At the risk of offending BKB, I would peg XL as the best balanced mod. The BKB mod seems to contain everything the author could think of throwing in it, which for the most part is fine. But as indicated above, sometimes it is almost too much.