For "60s blues and early 70s rock tones", there is probably no better option in AmpliTube than the
JH Gold, which is intended to model one of Hendrix's JTM 45/100s -- and which I strongly suspect specifically models one of the actual surviving Hendrix amps (as opposed to Marshall's own Hendrix reissue, the Super 100JH).
Slightly oddly, the
Brit Green speaker models in the
4x12 Closed 25c cab in the Hendrix collection almost certainly models a G12M (25w) 75Hz speaker, and quite possibly a modern versions of that, while Hendrix is thought to have favored the G12H speakers, 25w (or perhaps 20w) and perhaps
55 Hz speakers. The 55-Hz versions of the G12H (and G12M) were originally intended for bass cabs but also found favor with many guitarists. Alas, there is no IKM equivalent to the original G12H (though the various "Anniversary" speaker models probably model the G12H 70th Anniversary speakers, though these are understood to sound different than the original G12H speakers), but Celestion does actually sell IRs based on cabs with the reissue G12H (55) speakers. I am not a heavy user of IRs, because I actually like AmpliTube's "cab room"
, though I do have these in the 4x12 variant, due to my abiding love of early Marshall tones (and my unhealthy Lemmy worship
, as the 55-Hz variants of the G12H (or G12M) would have been used in the 4x12s of Marshall Super Bass rigs).
All that said, I seriously recommend trialing the
Satch Green cab from the Satriani collection, since I think it sounds better than the other cabs that use the
Brit Green speaker models. Also, it's worth noting that the
California Red speaker model (of the JBL D120F) that appears in the Hendrix collection's
4x12 Closed J120 cab model, having been used by, besides Hendrix, early Allman Bros., and probably some others I've forgotten/
Nevertheless, the JH Gold and the
Red Pig are the only "based on Marshall" amp models in AmpliTube that predates the mid-'70s. The JH Gold is probably closer to a "stock" Plexi circuit (insofar as such a thing can be said to exist) than the Red Pig (which is really its own thing), though I really wish IKM would release models based on "stock" Marshall #1959 "Plexi" and #1992 Super Bass amps -- because 1) they are again different, and 2) there can never be too many models based on vintage Marshalls. The Red Pig is underrated, though, I reckon: it still sounds like an early Marshall (of course) and has plenty of headroom, so besides being used on its own, it can be blended with the JH Gold (or other models based on earlier Marshalls) to provide a bit more variation (since early Marshalls were highly variable even when new, and scarcely became less so over the years). One weird thing is that the
Brit 80 speaker models in the "matching cab" for the Red Pig are almost certainly based on Celestion G12-80s, which were not produced until the later '70s (while the Marshall Major ceased production in 1974). I think this
may because Ritchie Blackmore (who famously used modded Majors)
may have put G12-80s in his cabs when they came out. Originally, I suppose people used cabs with some sort of "Greenbacks" with their Majors?
The
British Lead S100 is really an earlier attempt at a Hendrix amp; the JH Gold is effectively its replacement. Thus, the S100 is also similar to, but not yet actually, a "Plexi". However, it sounds similar to the JH Gold (though I like the JH Gold better, not least because it lets you do cool stuff like simulate jumping the inputs). But the S100 is another good option for "60s blues and early 70s rock tones" (perhaps alongside other amps).
The
Vintage Metal Lead is really (as far as I can tell) modeling one of the early (mid-/late-'70s) master-volume #2203 (pre-JCM800) amps. If you dime the master volume, however, it should sound a lot like an early "Plexi" -- and, indeed, sounds not unlike the JH Gold or S100 (otherwise the closest models to a "Plexi").
Those (above) are the AmpliTube models based (more or less closely) on earlier Marshall amps.
Thereafter, there are many fine Marshallesque models based on more recent amps that I won't nerd out over right now
though it may be worth mentioning the
SatchVM, based on the JVM410HJS Satriani signature amp, on which the green mode of the crunch channel is "inspired by a Master Volume JMP" -- which is to say, probably the same early (mid-/late-'70s) master-volume #2203 amps on which the Vintage Metal Lead is based.
And, then, yeah: the
Brit Silver is supposed to be a Silver Jubilee 2555, while the
JCM Slash is the Slash signature reissue (2555SL) of the same. As far as I know, there are no very significant differences between Marshall's 2555 and 2555SL, so the AmpliTube models can be expected to be pretty similar, too.