We have a large number of 1/16 tanks within the display team, ranging from basic Heng Long tanks, up to the Tamiya models. I would suggest looking at the Tankzone website. I have been dealing with them for some time and they offer a very good service. With complete models, plus many upgrade parts also.
The 27mhz Heng Longs are mostly phased out now and have been replaced with 2.4G versions, a bit more expensive, but worth spending extra for the improved reliability.
You can buy upgrade electronics by Clarke, available through Tankzone. These units start about £76 and replace all the onboard electronics with an improved control and sound system. You need to use a Tx and Rx of your choice at the same time.
Tamiya, you get what you pay for with Tamiya. Everyone should have at least one full option Tamiya model in their life at some time, I have, and regretted getting rid of it. Mind you, the clarke upgrades give you, as far as I am concerned, an 85% Tamiya spec for roughly 50% of the cost.
Horses for courses, it's all down to how much you want to spend, as well as how often you want to use the model.