I've only doubled on bass in bands, and the tracks I've played on bass for my recordings have been direct. I've never owned an actual bass amp.

I'd be interested in hearing why some players may chose cabinets with 15 inch speakers, as opposed to the four 10 inch cabinets, or I guess some have 8 ten inch speakers.

What's your preference?

My preference, personally, is based on the sound I want. The larger the speaker, and the more speakers you have, the deeper the response is. That can go to the point where you have a really really really deep bass cabinet that can sound somewhat muddy (which is sometimes desirable, if you like dub and reggae).

Personally I think a 4x10 gives the most stable spectrum of clarity and depth of bass response without muddy or twangy. Often, you'll be going though a PA system as well, so you shouldn't have to worry too much about volume when it comes to cabinets.

Right now, I'm using a Markbass 2x10 for smaller gigs (which is one of the best cabinets I've ever used by far!) and an SWR 4x10 for larger and louder shows. I haven't come close to needing both cabinets on the same show yet, thanks to PA systems and decent Front of House engineers.

Larger speakers are also going to have a more loose and slower response, which can also be desirable. 10's sound very tight and punchy.