That is very subjective.
Like pickups it is easier to do your homework, look at the manufacturers information, and pick an aftermarket speaker. Once you have chosen a speaker, install it and test it, then formulate how you now want to change the sound, you can come back to various forums and ask what speaker would change your sound in a certain direction.
The fairly new Eminence speakers are hot right now. Very good for the price. But, Weber, Jensen's, Celestions, all are good choices.
If it were me, I would put an Eminence Wizard in a Peavey Classic 50, and a Eminence Private Jack in a Laney VC30. The Laney is a little more Voxy, so the PJ would preform well with chimey treble, and the Peavey is reall more of a straight up rock n' roll amp, in that the Wizard would do well.
All opinion of course, and there are about a thousand other options that would work.
Another upside to these 2 amps is that they are cathode biased, not needing to be biased (They can be biased, it is just more work). So as long as you stay with mainstream tubes, they should be plug n' play. Cathode bias usually doesn't have a bias pot, but allows for a little play in teh bias circuit. Fixed bias is the circuit you need to bias for sure.
