For an HL tank Phil is the man to see.
As for which is better? The PIII is a great runner OTB and has many upgrade possibilities for sure. As for the Tiger 1, it can also be done to the nines and is a good runner, though I think it needs a bit of modding to be as reliable as the PIII. The track issue that YHR spoke of can be fixed with a tenisioner upgrade from Phil. They can really be taken as far as you want to go. these 2 tanks both have metal lower hulls available, as well as a ton of other upgrades.