After using the Thunder for a couple of months or so now I'm feeling that in some ways I prefer the original Hawk.

Shading:-
Both machines shade equally well, I haven't found the extra stroke length on the thunder has made it any better or worse in that department.

Packing:-
Both put in colour qually well. I've never thought the hawk was a good machine for doing stuff like tribal though, but IMO that's mainly down to the pins used in the cheyenne cartridges. Where as the standard t-tech mags with their medium taper will hammer solid colour in with either machine.

Lining:-
The hawk/spirit definitely requires a bit of adjustment to line with it or you can get weak lines and snags, but once you get it down they do it well. The Hawk was actually the first machine I loved lining with, and that includes coils.
The thunder on the other hand is much easier to switch to from other machines IMO. The extra stroke length has eliminated the occasional snagging when pushing your lines that the old machines used to have.
I don't think the Thunder produces a better line than the hawk, but it does require less adjustment on your technique.

General usage:-
I've had a year or so of loving the Hawk, I think its ran great on any PSU I've tried. A couple of the bigger needle groupings required a higher voltage to start, but not all the time, and its usually just a case if putting it on to my lining patch before going back to the shading one.
The thunder on the other hand has been a bit of a pain. Without the startup cable it almost always needs bumping up to around 12v to get it going. And even then it wont start if you have a lot of needle hang and usually also requires an on-off-on jumpstart.
With the startup cable it is better, but even that doesn't work all the time, so I'm still doing the on-off-on jumpstart on occasion.
Obviously it's supposed to work fine on the official PSU which might be my next purchase.



So in summary, I think for me I might prefer the original. It's quieter and smoother sounding. Runs easier on non cheyenne PSUs and performs just as well as I have already got used to using it for lining.
For people new to the cheyenne system I can see that the thunder would be the better option.. but only if you buy a cheyenne PSU.