I bought a Cx2 18 years ago for PPL and it is still working on the same set of batteries. I tried the manual E6B during CFI training and am glad I didn't have to use it. Gotta keep with the times...
That said an HP-12C calculator from the 70s will still blow anything else out of the water. Get the simplest computer that is allowed, know it inside and out, and you'll be fine.