Dremel if their nails have been kept up pretty well, otherwise a combo of nail clippers (safari brand is excellent, using it on my current pup) and the oster lithium ion dremel. It's cordless and rechargeable, has two speed settings. I have no complaints, though it could be loud for some sound sensitive dogs. The combo of the two work nicely when you're dealing with nails that are a little long because you can cut them down a bit with the clippers and round off the tips with the dremel without being afraid of hitting the quick.
Rocket (pomeranian) - 01/2002 - 03/2016
Hircine vom HausReid "Sawyer" (GSD) - 11/24/16