1.) Harsh highs. None of the 4 Ubers had harsh highs in any manner, and all 4 amps would easily be "dark" by my standards. The stock TJ was the brightest of the bunch, though once again, this is splitting hairs. None of them were overly bright. I've always run =C= el34s in the blue, never anything else.
2.) Flubby lows. The 2 was "the loosest" of the bunch, especially on a 7 tuned to A, but not in an unpleasant or unusable way, it actually worked quite well for the over all sound/feel. None were VHT levels of tight, though none were in any way flubby or farty. Only when EQd like a 12 year old at Guitar Center did any of them sound flubby and loose. Proper gain/EQ settings provided solid, articulate lows. When EQd for the guitar being used, all had acceptable low end response. None of them sounded as good through the Mesa nor Marshall cabs we had laying around. The mesa sounded the dullest. All 4 sounded tighter and more articulate with the uberkab (real loaded, didn't have access to a front loaded and still haven't tried one).
Once again, all 4 amps sounded extremely similar on the 2nd channel, when EQd to the guitar being used. Going from a 7 with EMGs to a 7 with Crunchlab/liquifier combo to a 7 with blackouts, and a 7 with custom wound 1 off pickups, produced far more variation in sound than there was between the amps themselves. What I mean, is we'd go through with 1 guitar, and I'd pick out (blindly) which of the 4 I preferred (a, b, c, d, etc). Then we'd change guitars. Each time we each had different results. There just wasn't an over all winner, nor a massive difference between the 2nd channel on the 4 amps. Certainly not as massive as going to an entirely different amp we had available (modded marshalls, mesa's, axe fx, oranges, herbert, and more).
I certainly wouldn't put down any of the various styles of ubers based on what I've experienced with any of them, nor praise any model higher than another. I think you'd find nearly as much variation if you played 10 TJs, or started swapping Pre/Power tubes and cabs, as you would going from a 2 to a Blue to a TJ, on the 2nd channel. Certainly could have been a case of the blue being an exceptional example (it's an early blue, when they still had Symbol serial numbers and an attached power cable), or that any of the other ubers may have needed servicing, or had sub-optimal tube compliment, or just been a lemon. Some amps are just lemons, working at music stores long enough, etc, you experience it. You stock a bunch of the same model, and some just speak to you, while others don't. No way I'd put down any of the uber variations based on those experiences. Ubershall's rock, period, in my book.