I would fastrack rattlesnake, but I find its always a good one to run to first thing as everyone goes straight for fury or vampire. Also, from there you can run to tomb blaster and rameses without massive queues.If you have to then I, too, would go for this fastrack. If you can (not sure if it's on their "one shot" fastracks) I'd add Rattlesnake on also.
Having said all that though, I don't condone the use of fastrack and would say to avoid it if you can. But each to their own
And I agree about fastrack. I hate the fact it exists and it allows people with money to queue jump, but Im prepared to lower myself to that level if it means I can get the two decent rides done without waiting two hours for each. And Chessington aren't too badly priced for fastrack compared to some other parks.