What size do most of you like for a general "all purpose" BC reel?

150

The 150MGL is fantastic for almost all presentations IMO.

I fish both and I find that I prefer the 100 for palmability.  The 150 isn't that much bigger, but its noticeable side by side.  That said, if you're running 17lb diameter plastic lines (US sizing) or 20 lb (JDM sizing) go with the 150.  The smaller 100's don't hold quite enough of the bigger line.

My reels need to be dual purpose so 200 sized for me. I do however, have one 100 sized curado. 
 

If I strictly fished bass then I think I’d like a 150. Line capacity is very important to me because I am a shore angler. If I’m forced to make a few long break offs from snags and such, the reel is now in a less than ideal condition and useless to me for all intents and purposes (casting distance, retrieval rate are compromised). I don’t have the luxury of floating up to the snag to minimize loss of line from a break off. 

I typically dont notice a LOT of difference between them, or even necessarily know which are which in some models.

 

I have an SLX, but dont know if that is considered a 100 or 150. I have a handful of SLX 71 K models and a Curado MGL 71 I use for anything from poppers to jerkbaits or light texas rigs, a couple 6spd Curado MGL 151 models I use for crank baits, and a couple old Calcutta 101s I use with braid for Chatterbaits.

 

I'm not a long caster so spool sizes don't have a big impact on me, so to me, either works. I'd say if you use heavier lines for long casting, maybe go with the 150, otherwise either will be fine.

I rarely use FC over 17lb, mostly 12 and 15 for FW bass.  The 100 has plenty of cap for me.

I hope this doesn’t come across as ignorant or uninformed but which casting model Shimano comes in a 100 size? I only have 2 Shimano casting reels which are a SLX MGL 71 and a Curado 151 MGL which much like @FrnkNsteen I feel have more than enough line capacity for my fishing style, but I will add I own a 100 size Daiwa Tatula and (2) 80 sized Daiwa reels that both hold more than enough line for my style of fishing. It seems to me at least the Daiwa’s hold more line than the equivalent sized Shimano’s in the first place if that makes any sense. 

For Shimano, the first baicasters in 100 size go way back to the first Bantam (1979).  And there is no equivalent size between different makes.  One company's 100 may be bigger or smaller than another company's 100.  You can really only compare between reels of the same make.