Competitively, Swampert is the best. there is cursepert, roarpert...lots of different names and sets. Swameprt has tremendous stats for tanking. Grass types, even if you have ice beam, murder the guy. Most grassers are faster and can withstand an ice beam. Ice beam seems to come in handy when mence pops in.
Sceptile is a nice subseeder, but really isn't anything of a great sweeper. It really isn't a good sweeper at all IMO. It doesn't have the power, unless you power it up somehow .
Blaziken is probably the worst. It has a base speed of (lol) 80, so it can't really make use of its awesome attacking stats. When you scarf it, it's okay, but it is still outclassed by infernape. If we're talking 3rd gen, Mence or Nite are better mixed sweeepers, heracross pwns it as a physical sweep, and Zam is a far better special sweeper. It is also weak to EQ and water attacks :/
From a coolness standpoint, that's only personal opinion. I prefer swampert, which is also why I use it on my team :)
EDIT: SuperKyogreRuler, for the record, your logic on swampert is a bit flawed :/ Swampert's goal isn't to cover types, it's to tank, tank, and tank some more. Not to mention counter TTar and other pests. Besides, supereffective (I can't stress this enough) isn't everything.