My vote goes to Bouffalant.
The one thing I really disliked about BW was taking out all of the old Pokemon and replacing a fair number of them with obvious ripoffs (Conkeldurr, you're not fooling anyone). I think if those ripoffs hadn't existed, BW would have a percentage of good designs comparable to first-gen (or maybe even third, which was the best of them all).
That said, Bouffalant is an exception to the rule. Unlike most of the ripoffmons, his special gimmick actually WORKS from a design perspective, meaning this is an actual contest here. Let's look at the points.
DESIGN:
Tauros and Bouffalant have similar color schemes and muscular bodies indicative of great strength - no clear winners so far. Looking at the individual features, however, puts Bouffalant squarely ahead of his counterpart. Being a long-haired male myself (although it isn't an afro), I'm a sucker for any Pokemon who looks manly with an unusual hairstyle. Bouffalant's forbidding yellow eyes and gold-ringed horns are just the icing on the proverbial cake - the mighty AFROBULL wins, no contest.
BATTLE CAPABILITY:
This can't be determined as easily. Bouffalant has more raw power and superior bulk, but Tauros has a Speed advantage crucial for offensive Pokemon. Bouffalant is arguably a bigger threat to face in the BW era than Tauros is (CB Afro Break gets a clean 2HKO on 248/0 Escavalier after a Sap Sipper boost), but the old-timer was one of the top five most-used (and most dangerous!) Pokemon of OU in his day. Tauros comes out slightly ahead in this area thanks to his achievements in days gone by - something to celebrate as he drinks away his sorrow and gazes longingly at his old crown (heh).