i would say sports cat but a high flow one, that way no hassle with MOT's, police etc.
Ive just bought a decat but have the premises etc to swap it back whenever.Have also bought a O2 sensor spacer from usa ebay to eliminate the eml light problem will be fitting it on saturday
decat, much cheaper
Unless to get pulled for a road side check
Just get to know your local MOT place, they will then pass it anyway.
And are the police really going to go to the effort of getting on their hands and knees to have a look under your car with a flash light to see if you have a cat or not?