I have no idea about "best", but I picked up an 8100 cordless a couple of weeks ago, and it has worked perfectly for Gusto. I had people tell me the cordless wouldn't last long enough, but I got all four feet done 3 times (trying to get his nails shorter, so I'm doing them every other day) and it was still running fine when I recharged after that.
And I have to say, getting it was a fabulous decision. I could not get Gusto's nails shorter with clippers, and he was starting to hate me for trying. In 2 weeks, his nails look better than they have in years. He likes the Dremel SO much better than clippers.