I’ve only been to the 2011 race, but I was seated at the K1 grandstand and can attest to the awesome view it provides of the main straight, pit lane, pit exit and turns 1, 2 and 3. You can see 4 in the distance if your seats are high enough.
Given that the majority of the overtaking was done on the main straight (courtesy of DRS), the K1 stand gives you the one of the best views of the action. It was pretty awesome watching Webber bang wheels with Massa through turns 1 and 2.
If you purchase your tickets early enough, you can get them at half price which makes it even more of a bargain. Well worth it given that it’s covered and hence protects you from the burning sun and torrential downpours.
I’ve heard good things about F Grandstand. If you take the southernmost seats, you’d get a great view of both straights, while Turns 7, 8 and 15 are no contest. That said, this is coming from someone who’s only ever been to the North Grandstands.