Marshall Models (Page 2 of 2)

Any of them if you have the chops my man!  I would probably go for something with bigger tubes myself because I think that EL84's in Marshalls definately change the sound.  EL84's are more Vox-y sounding with KT66's or EL34's being the quintessential Marshall sound.  Could I suggest the JTM45 KT66 model? I think that would EASILY cover the Clapton/Hendrix/Page stuff and is about 30watts (same as the Bluesbreaker but in a head form).  Not too loud for home use but plenty loud for most gigs especially if you mic it.  One of the best amps I've every had the pleasure of playing was an original  white '62 Marshall Bluesbreaker.  The fattest, creamiest, and most complex cleans/distortion you've ever heard.  Just shoot Nik an email and ask him what tone you are looking for and the application (home/practice, studio, gigs, stages) and he can suggest the best amp for your situation.

"Is the 20 watter a baby brother of the 50 watt plexi?" 

Yes and no.  Yes in that it has TMB and is a Marshall, no in that it does not use the same tubes and has a different circuit.  The 20 watter will obviously have less headroom.  You mentioned that you have an AC15, are you planning to pair the amps?  If so I would try and match wattages as close as possible.  If not, I personally would opt for something different than the Vox (EL84s).  A 50 watt plexi would allow you to choose either the 1987(lead)  or 1986(bass) circuits.  I would say you can't go wrong with any of them.  I think the major issue would be to find the amp that breaks up at the right time for the application you plan to use it in.  I currently run a Dr.Z Mas JR (EL84s) with a Hiwatt Bulldog (EL84s) and a stereo attenuator that allows me to either play them at TV volume or at full gigging volumes.  I like having amps that can cover both applications well.