Re: Marshall 1959HW Handwired Plexi vs JCM vs JVM heads?
Assuming you mean an original 1959 handwired Plexi and not a new/recent model with that name, the biggest thing you'll find about vintage gear is that "they don't make 'em like that anymore, so that's why it's better". It's the tone of this acclaimed guitar hero and that Top 100 Of All Time song's guitar tone and all manner of screw-countng, cork-sniffing excuses.
It will always get great reviews from:
1. people who vaguely remember having an original one many years ago but sold it to fund the wife/kids/house
2. people who never had one but know to associate "Plexi" with "Hendrix" and "EVH", and swear they're nailing Wind Cries Mary and Eruption in their basement through their bootique 4x12
3. vintage gear nerds who think everything made before they were born (or when, if they were born before Hendrix or Elvis died) was perfect in every way.
4. the small percentage of the bedroom/basement/Blues Lawyer population who can afford one, simply because they have something you can't afford.
If you mean a newer model named "1959HW Handwired", then see points 1, 2, and 4 above.
The JCM800 was an instant favorite in the early 80s with the Hair Metal crowd because it was a Marshall with built-in distortion, rather than just loud enough to brush your hair. You didn't have to punch holes in the speakers like Clapton did with his Bluesbreaker. You could also stick these relatively new "pedal" devices in front of them and increase the gain for those super-wankery meedly meedly scalar runs like Lynch and Rhoads, and still kinda sound like Hendrix, Blackmore, Page, or early EVH without them-thar pedal-thangs.
The 2203 reissue was billed as "same amp as before, but with an FX loop" according to the literature I looked up regarding my JCM800.
I will say this - the 2203 JCM800 is LOUD. If you can't be heard with it, you're doing something wrong (playing to the dead or deaf). Not really enough gain for my needs, though, so it can benefit from having something in front of it - pedal, rack preamp, etc. Definitely gets a nice Angus tone by itself, but not so much for anything heavier.
No idea about the JVM, but once you start crowding more circuitry into a head, you lose that "classic geetar into amp" he-man tone that says you've got an armadillo in your trousers.
However, you gain a rack's worth of tonal variety in one package that is relatively easy to carry.