I have a HL P3 (converted to Tamiya electronics) and from Tamiya: 2 Tigers, KV, and currently building the Panzer IV.
The 3 Tamiya tanks I have built i believe; you can't really go wrong with either one of them for straight out of the box builds.
The Tiger is a great Tank, and will perform great, plenty of room on the inside to run 2 batteries in it.
The KV-1 is a little tight on the inside, but has great sound and even comes with lights.
The Panzer IV is about the same size as the HL P3 and not much difference there, excpet for the detailing that comes with the Tamiya Kit.
Would be interesting to have the HL P3 and a KV-1 as these tanks would have fought each other in 1941 and 42. So might be a good contrast in size for ya. And if ya wanted to eventually battle the tanks against each other.
Just my humble opinion.