As was said earlier, the 77 is an excellent gun all round , but, the Superstar is very good too.
There's a few different opinions about the long transfer port through the rotary breech and some don't like the trigger but once again it'll be down to personal taste. I've shot a lot of guns with Rekord triggers that are badly set up but the owners didn't complain.
There's talk of the break barrel BSA guns having 'issues' with the bore where they were brazed to the breech block but the Superstar and Goldstar won't suffer with this (that's if there is a problem in the first place)
I'd guess that if both guns were put head to head, the 77 would come out on top but the Superstar is lighter, the finish was very good and if it went horribly wrong, you can't chop the end of your fingers off in the breech
I like to buy Blitish and have a soft spot for Brummie guns so I'm slightly biased
With new breech O ring, a new piston seal, ( I've found the black BSA seals can sometimes look like new but still be worn, so tend to replace them in a new to me gun ) and a good cylinder polish and lube can make for a nice smooth shooter. I made a steel top hat weight, used a bit less spring and a Webley 'clothes peg' spring guide in my last one and it was sweet as a nut. Superdomes were the pellet of choice in that one (.22) but I think FTT were good too.
The 77 may be a bit more pleasing to the eye and is deadly accurate when sorted so if in doubt there's always the option of buying one of each, just in case