It depends on what you're like, for example with me, I can be lazy however in the right environment I can be very successful and hardworking- so sixth form was the best option for me!
I'd personally recommend sixth form because if you work hard now, you don't have to work as hard later (in life)!
if you would rather have a more 'chill' 2 years, then college is probably better!
just make sure you find a place for you and you're happy- bc at the end of the day thats all that matters!