As far as what is 'considered' standard, based on film size, it would be the 90mm, the 105 was an option that was chose on several of these cameras when purchased new, the difference is very close to what Minolta offered several years ago, when they were including a 45mm as standard and the rest of the industry was doing 50mm, as far as quality and field of view, the noticable difference in real world shooting is really not going to be that noticable, the 90 and the 105 are both very good quality shooters and you should be happy with either of them, as was said, use it to your advantage and buy the least expensive of them.
Dave