Difficult group for me to pick from, as I've only been on half of them: Hyperion, Lisebergbanan and Stealth. I really like 'banan, but I don't think it's quite good enough to progress from this group.
Based on the GCIs I've done, I'm confident Thunderbird is an excellent ride. To be honest I find it very difficult to separate them all in my rankings, though there are one or two that stand out for good or bad reasons I expect this one to be somewhere in the middle. Not quite good enough to go through.
I'm going to group the Macks together - I've been on neither but done Alpina Blitz and Icon, Helix and Blue Fire so have a pretty good idea of how the various types stack up. Helix is of course phenomenal and Blue Fire excellent as a package but purely as a coaster has too many dead spots (final roll is the highlight). Alpina Blitz is the Mack take on a mega lite, and does an excellent job so would be my pick of the two in this group.
Having ruled out the others, my votes therefore go to:
Stealth, which is one of the best Intamin launches out there (behind TTD but ahead of KK). Having been on Xcellerator for the first time this year I'm no longer so sure it would benefit from being longer either.
Finally Hyperion, maybe not quite as phenomenal a ride as Intamin are capable of delivering from this ride system (it's no Skyrush), but still easily one of the very top coasters in Europe and easily the best coaster in this group.