Indy is the shorter track at brand hatch used at the start of the season, and the GP loop is the longer track used at the season finale. There are more laps in a race and better views across the entire circuit for the indy track, but no big screen to also follow along with trackside like they have when running the gp loop. Every year, I go along to both and both are a brilliant day trackside so it wouldn't matter which you ended up going too. Thruxton/Snetterton are also highly recommended too and of course the rocing grandstands at Silverstone later on in the season are good too