Well I had a Janspeed on my old F which I alternated between having a decat or when it came round to MOT time a bog standard cat, but either way it sounded great. The Janspeed is perfect if you want a car that sounds meaty but not obtrusive or boy racer however when you put your foot down it gives a nice roar!
Alternatively I'd recommend a Blue Flame (
http://cgi.ebay.co.uk/BLUE-FLAME-CAT-BACK-EXHAUST-MGTF115-120-135-160-/310227170149?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item483afaf365
) which sounds just plain sexy or Daytona (
http://www.mikesatur.com/acatalog/Exhaust_System.html
). A lot of owners also have the Miltek which although I found a bit too loud it is still a quality exhaust.
As for replacing your cat I personally wouldn't bother with a sports cat as although they are good they are often a hell of a lot more than a bog standard cat. Have you had a look at the condition of your exhaust & cat? Only they can be a nightmare to get off if it's the original so I'd start lubricating now! :naughty: