www.rocksolidamps.comlots of ENGL sound clips on there (mostly death metal, but theres some REALLY good clips of the Thunder & Screamer doing Satriani and Vai stuff).
Cant go wrong with any of them, i have a Fireball and theres a couple of Powerball owners here, and Tim has a Screamer..
Never played a Thunder or Screamer, but i believe (from lots of research!) that the Screamer is a bit more vintagey sounding when not in balls out face melting gain territory and really versatile, and the Thunder is a no nonsense plug and play kick ass rock amp.
The Fireball strips wall paper with the gain on 10'o clock :P
Its madness!
Brilliant amps for the money :)
I didnt go for the Koch or the Riveras (i looked at them before buying my Fireball) they are nice but (for me anyway!) they arent the right amp, they arent really metal amps... the Koch does have LOTS of features, including an attenuator and recording outs... which may be what your after... not really a 'this is my only amp for everything' choice though imo.
Depends on what you need really, for the music you play. My money would go on the Screamer or Thunder from the choices, i wouldnt touch the Laney though... didnt like it when i played one!
They are all very good amps, but its down to what you want... as i said the Engls gets my vote, can do classic rock to death metal so you arent limited... are good value, and look really cool 8)