Hey, Marc, you're in pretty much the same place I am, as far as what you want from your tank. Realism is first. The first thing you need to ask yourself is, do you plan to battle with this tank? If so, then you'll definitely need IR and Tamiya compatible electronics. I'm not sure about Tamiya, but none of the other tanks have proportional turret rotation or gun elevation. As far as I know Tamiya is the only one that comes stock with up/down elevation as compared to a set cycle (goes all the way down, then all the way up, no changing direction mid-cycle).
I couldn't make up my mind so I have both, IR and airsoft.
I started in static modeling many, many years ago so I also like to build, and I've done a lot of upgrades to most of my tanks. If you're not going to battle and you like the modeling part of it, I'd recommend the Taigen Tiger One Airsoft in all plastic. I have one of those (my second tank purchased) and I've had incredible fun turning it into a totally different beast. This is my plastic Tiger One right now, and I'm having a blast with it. It's had tons of metal upgrades so it's almost a full metal by now.
If you don't care so much about modeling and you want the option to battle then the Taigen Full Metal Tigers are pretty cool. I have three of them, so I guess I like them.
They're great runners right out of the box and if you get them in IR they're easy to add a Mako unit and go battle with the Tamiya crowd. They have the 4 shaft gearboxes so they're slower and act more realistically (in my opinion). Or you can get one in airsoft, but I think the very best way to go with that tank is to get the IR version and then get a metal airsoft turret to go with it. Then you can have the best of both with a five-minute swap of turrets.
Of course, if you have the cash they do say Tamiya is the very best. Sean (panther commander) has a great Tamiya King Tiger for sale right now that you might want to look at.
There's lots to think about, but it's good to see a new tanker and I hope you find what you're looking for and most importantly of all, that you have fun doing it.