#1
Which should I get, a Ceriatone 50 watt Plexi or Ceriatone JCM 800?

I play mostly:

Van Halen (early albums)
Guns N' Roses
Led Zeppelin
Ozzy (Rhoads era)
AC/DC

Which amp is the most versatile and cover most of these?
#2
A plexi is perfect for those, but you'll need an attenuator to get the gain needed for.. just about all those tones.

I'm not kidding, they're loud as hell, and unless you cut one of the bright caps, will max out in volume before you even get any breakup.