I'd personally always choose Ashley over Sportex
But as Skymera said pretty much personal preference, you won't see any real gains just more noise
Ashley sound:
Sportex sound:
Sportex are renowned for being quite 'boomy' exhausts. They aren't that raspy sounding but are generally a little bit louder. Saying that, Skymera's sportex sounds pretty good!
EDIT: I forgot to mention if you have a bit more cash you might well want to check out the Peter Lloyd system
Personally this is my favorite one, proper raspy rally sound and I think it comes with a centre decat (replaced by a silencer by the looks of it?). Again I haven't used one personally but by the looks of them they are from the downpipe back. They're about £40 more than the sportex and ashley and don't have pretty tips either.