pic, i have an epi valve jr. head-have had it maybe 3 years. i like it....with 'the wrong' speaker cab, it sounds bright and harsh. with the 'right' cab, it sounds smooth to my ears. now that i have established that i am a 'tone crazy', a couple years ago, all of my disposable income went to 'new raw speakers'. i think i bought maybe 6 new eminence, jensen and maybe a celestion, and made cabinets out of 3/4" plywood for all of them (which i had in the shop). the 'smoother ones' (again, to my ears, which are a little bad nowadays) were the eminence copperhead, the cannabis rex and the jensen jet tornado.
both companies have sound bites of their speakers; there is also a youtube vid by rivera amps, i think, which compares a wide variety of speakers. the modders try to stick different brands of el 84s in the epi, and claim all kinds of success. i don't notice as much difference with a different tube as i do with a different speaker. right now, i'm running a celestion 12" (i think the 50 watt) on mine stuck in the original epi speaker cab. sounds pretty good to me, but the fact that all the larger speakers are way higher in wattage than the epi can reach restricts any speaker overdrive. i have to overdrive the amp to get decent grit out of it.
dunno if that's helpful re: epi valve jr.; just one person's experience. reliable amp, though. actually pretty well made and very cheap (mine is a clearance for the new version one).