Re: So who is the best candidate?

"Needs to be able to edit DPX, XDCAM, DSLR."
Both Can do that.

"*Work with Resolve"
I haven't heard of Ppro successully doing this.. so I'm not sure. Resolve is supposed to support AAF... while AVID's AAF export seems solid, I haven't had a single successful AAF export from Premiere myself.

"*Footage will need to be sent for compositing in either Nuke or Fusion. Rarely After Effects."
AVID will be an advantage here, since you could get your artists to encode straight into DNxHD format. Premiere doesn't have it's own "format" ... which can somewhat be annoying when picking a format to render to and not wanting to say "uncompressed". The DNxHD codecs are a free download for all users, whether they own avid products are not, mac or windows -- it's all the same. Of course... you could always import those DNxHD files into Premiere ... but you wouldn't get the same real-time performance that way.

"If it matters, applications such as Maya, 3DS Max and Lightwave are often used in such projects."
Same advice applies here as above.