What you buy is to a large extent dependent on where you live,
If you view the sidebar you will see that I am from England whereas many members of the Forum are US or Canadian residents so if you are from the US or Canada I would not recommend HENG LONG but suggest TAIGEN/TORRO because probably the best supplier is "IMEX" and "ERIK" is a member of that company and an extraordinarily helpful member of this Forum as well.
As to Tanks The HENG LONG Tiger 1 is a favourite choice of many of us BUT beware of the HENG LONG PANTHER, The company when they began, to save tooling costs they designed a Pantherish body to fit the Tiger 1 Hull, IT IS NOT A PANTHER, in the hobby it is called Politely a PANTIGER more honest people call it an abortion!!!
TAIGEN make both a Real Panther as well as the Jagd Panther and both are nice replicas,
HENG LONG have discontinued making I/R Tanks,
Within this hobby there are some very competitive souls who worldwide enjoy I/R Battling which is why there are some rules on equipment and basically you have to fight using TAMIYA compatible I/R kit to be able to use your Tank in club battling BUT there is nothing to stop you using any I/R equipment you own for your own fights.
Different Tanks made by the same maker in only rare cases share hulls, although many internal parts are the same such as R/C control boards /smokers/and sometimes gearboxes but there are not many interchangeable parts between different types within a makers range, Panther and Tiger 1 tracks are different in length but are the same otherwise, a number of parts from the PANZER111 are interchangeable with the PANZER4 but you really need to ask someone on the Forum if you are in doubt as to what will fit and what won't. I hope that helps.
shaun.