Picking the right size is difficult. I have a large, and often times I wish I had a medium and an XL as well. The large is overkill for a standard 2 person dinner, but it does well with 20+ lbs of turkey, pork shoulder, ribs, etc.... The XL will use more charcoal than the Large, but if you are always cooking enough to overfill the large, then you are better off with the XL. If you are looking to do the entire meal on the grill, maybe lean towards the XL, but if you are looking to do just the main dish typically, go for the large. There are also option (from BGE and other places) to increase your capacity, change the distance from the fire, etc...
I have done everything from smoked ribs and brisket, chicken (wings, pieces, breasts, whole, spatchcocked), 24 lb turkey, burgers, fajitas, veggies, potatoes, fish, to seared steaks and 3-4 minute pizzas (personal sized ~10"-12"). I'm not familiar with tandoori cooking (heard of it, but not really sure of the process) so I can't help you with that one. I still want to try bread, setting up a cold smoke system, and a host of other things.
If you want some more detailed help, feel free to ask (there are several eggers on here) or visit the big green egg forum.
It seems to me, that about 90% of people that have tried a big green egg love it. The other 10% should stick with gas grills and the kitchen stove (or maybe even the local steakhouse).