There are good arguments for both actually. The ODE physics engine in A7 (and A6) is good, but has it's small flaws of trickiness and tends to be slightly slower than Newton. (don't know how this is in A7 though!)
Still, in my experience Newton is a lot more difficult to set up properly because of having to include all the necessary dll commands. Newton is probably faster. The A6/A7 physics engine does a pretty good job, I tend to favor that one over Newton because it's a tad easier to use (simple engine commands) and I do not require massive amounts of physics objects and even Newton fails at some point so it's not a huge advantage.

What it comes down to, use what you like, there's no real winner both are good considering what they offer, especially since both are now *free. (*unlimited physics in all editions now with A7, right?)

Cheers