my own opinion lar, if u take d5100, if u plan to buy the 50mm prime lens f1.8d, which is the most beginner would try on, u have to use it as manual focus only.
as d5100 does not have body AF build in have to rely on lens to AF, things different in d7000, u can see the different in the mount



you would notice the small 'fella' on the bottom, which drive manual focus lens, open up more possibility to Nikkor lens,
thing is different in canon.