I've always thought that Buffy's preference in weapons, as well as her basic tactics, were more due to her teacher (Giles) rather than anything else. Giles could be compared to a martial arts instructor, in that he would almost certainly teach what is most familiar and efficient in his experience. Just like no two martial arts instructors, even if they teach the same style, they almost never teach exactly the same thing. Giles obviously preferred weapons that might be considered the traditional Slayer weapons, those that had proved their worth over centuries.
Wes, just as obviously, was more open to innovation and non traditional weapons, most significantly firearms and the sleeve sword that he seemed so fond of. Probably, Wes only gained his knowledge of and preference for more modern weapons first during his rogue demon hunter days after Season 3 of Buffy and before coming to work with Angel.