I actually have all three of those cabs. I have been using the 212 by itself and the 210+112 together. I have also used the 210 and the 212 together. Here is my brief synopsis on each cab. 210- Tight and punchy cab. Made to project the mids. I get lots of highs with the tweeter on and excellent compliment to the other two cabs. Lacks a little on heavy low B playing. Notes lose their authority. If you don't play 5 string this is a nice cab for you. 112- Nice single cab in that it can handle a low B and still produce solid mids. Can be a little deep though and if EQ'd properly this cab can be pretty versatile. Paired with the 210 this is a formidable small stack. Many guys on Talkbass run this setup. 212- Loud and solid cab. Can handle lows easily and can still bring some punch. Mids have to be added depending on bass and head. This is a nice single cab and can do almost anything. This brings what the 112 can't, volume. Mixed with the 210 which I have done at times, the whole spectrum is covered. 210 handles the highs and the 212 brings the lows. If you need a single cab go with the 212. Best of the three and loudest. If you want portability and versatility, go with the 210+112 setup. Then whenever you need to you can just bring one of the cabs when needed.
What kind of guitar and style? I'm considering a 2x12 8 ohm neo myself to go with my 2x10 8 ohm neo - for a 4 ohm load total. (The 1x15LF Eminence Delta I currently use with the 2x10 neo doesnt match up very well efficiency-wise, the 2x10 overpowers it) I think with a 2x12 neo my power will be more evenly distributed, and the same type of speakers will help. Maybe shoot for an 8 ohm 1x12 and a 4 ohm 2x10 if your head will handle it (~3 ohms) - you will have equal power distributed to each speaker (8 ohms each speaker) Others, is this the wrong way to go?
I don't think the Mag300H goes down to 2.67 ohms. If you already have the 210 then get the 112. You will immediately notice the difference when you hook it up.
This is my exact rig (although in an unusual configuration: I run a dual mono setup with a full-range clean signal to the 2x12" and an effected signal to the 2x10") and I can't comment enough on how incredible happy I am with it. It fits my unorthodox setup perfectly as the 2x12 covers the full-range "bass" with the perfect balance of punch, low-end, and clarity, and the 2x10 w/ the tweeter cut works perfectly as a smaller "effect" cab for distortion, synth, and other effects. Of course, even though I'm running dual mono and could have picked two 4ohm cabinets for "better" power usage, I went with the 8ohms because should I change my mind in the future and want to run bridged mono, I'm in a much better position to do so. Feel free to PM me with any questions, but I'm not sure I can add anything to the above (other than what I've written on my site) - if you've purchased from Dave before you already know about his outstanding CS, and I'd certainly put him first on the list should I need additional/upgraded speakers... but the only thing I can imagine right now is when I start gigging on a regular basis, either a 4x10" Neo or tolex/liner-based coverings might be a worthwhile investment.
Nice setup! Hmmmmm maybe I should follow your idea and use the "Rick-o-Sound" feature of my bass, use the 212s for the neck pickup and the 210s for the bridge. Id need another yba200 though. Ive been on a simplify mission lately... and now this... GAS pains... LOL