Since I own a couple........
Were I looking at middle of the road priced Thunderbirds my choices would be these three and I'm listing the in order of my preference.
'88-2000 Gibson, shallow neck pitch, fantastic slim neck (much like my '64) great players. Don't be afraid to modify them, this one's had all of it's hardware changed out, pickups are from Mike Lull, the first Thunderbird repro pickup on the market.
Any Greco Thunderbird. These things will tear your face off...........Easily the best non Gibson Thunderbird at any price, a II (single pickup) is really the one to find.
Epiphone Vintage Pro, or '60s Thunderbird, a nice Bird at a great price, the neck is a bit bigger than a Gibson and the pickups are a little tame compared to the Greco, still a really good Bird.