exhaust question

hi all i have an a3 2.0 fsi 04 plate with a rattle on low rev acceleration 130k
i am hoping that i have a damaged cat(not a damaged engine) which is rattling and also the car seems underpowered slightly
i know the fsi is not fast anyway but had same problem on a vectra v6 changed the cat and went loads better
my question is
if cat is gone what is
the best way to proceed

standard cat ?
sports cat is it worth it ?
or decat is it worth it ?

thanks guys