Re: What's a good 10" speaker?
Which frequencies do you want to emphasize, and which do you want to reign in? Do you want the speaker to add cone breakup or to add very little of its own distortion to your tone? I've found that others' recommendations are good to get me in the general ballpark to find what I'm looking for, but in the end I just needed to buy a speaker, try it out, try another one, compare, repeat.
Now, having said all that, I've tried and enjoyed a few different 10 inch speakers all for different characteristics they had. First off, I have never used any alnico 10's that could handle more than a mouse fart for power, and all these low powered alnico's tended to have almost zero bass but lots of raspy treble. For me, I like ceramic 10's.
Eminence Lil Buddy
I used this in an Epiphone EA-33RVT Galaxie (same as Gibson GA-17RVT Scout) 8-10 watt tube combo with open back cabinet. I found it to be pretty full frequency. Healthy lows and mids. Highs weren't exactly subdued, but not sparkling either. No noticeable cone breakup.
Eminence Copperhead
Used in the amp mentioned above. Less lows than the Lil Buddy, but still good. A little upper mid honk which I really liked. Brighter than the Lil Buddy, but not at all shrill. No noticeable cone breakup. I really liked this speaker in this amp.
Eminence Ragin Cajun
I used two in a sealed back 2x10 cabinet. The most notable characteristic I remember is these were very...I don't know...efficient, aggressive/fast response, very present. The sound was just kind of BOOM here I am just leaping from your speakers. I like a more relaxed response, so I moved on.
Jensen MOD10-50
Also used in the sealed back 2x10 cab. A lot more low end than I expected for a 10 inch speaker. I drove this cabinet with a mid-70's Traynor YBA-1, with both guitar and a P-bass, and often in to overdrive. These speakers never crumbled or farted out. They're a little scooped in the mids. Highs can be pretty bright. I think they're very good for a mid scooped "Fender" tone. The cones will break up fairly quickly, and the breakup is rather crunchy and a little raspy. Efficiency is on the low side, so you can crank your amp up and not blow your eardrums out like the more efficient Eminences above.
Celestion G10L-35
I had a quad of these in a Marshall 1965A angled cabinet. Also pushed this cabinet with the aforementioned Traynor YBA-1. I just loved these speakers both clean and overdriven. They are low efficiency, they don't have much low end, cone breakup comes on fast, and the breakup has just the right mix of crunch and warmth. Again, the lows are kinda weak and loose, so use 'em for blues and classic rock, but not metal.