Over the years, I've had tickets for several grandstands.
T23 (Maison Blanche) : sat there for years, which for me still is one of the best grandstands to sit and take pictures as you're able to shoot over the fence and the sight at night when the cars are going on to the main straight is still one of the best at LM.
T20 (Leonard) : was there last year, good view on start/finish, Ford chicanes and podium. Sucked for pictures (as do most of the grandstands on the start/finish)
T34 (Stands) : been there for a few years, for me a great view over start/finish straight (you just miss the pitstops), podium and good to shoot from. When the crowd thins out, you're right above the action in the pits on the front row.
T05 (Dunlop) : no comment needed I guess
T04 (Panorama) : good view, but sucks for photography as the fence is too high. Dunlop is way better 'cause you can shoot over the fence
T14 (Barnato) : good view on start/finish, exit pitlane and onto Dunlop chicane but sucks for photography
Always booked grandstand tickets so we wouldn't be in the rush to get a good spot at the start of the race, and get a place to be out of the sun/rain. Also at the evening, when the night starts to set you'll get into almost all grandstands if you have a ticket. Spent many nights in Dunlop grandstand or stands opposite the pits.
Don't panic if there are no tickets available anymore at the ACO site. Last year tickets for T34 were still sold at the shop in the museum on Wednesday and Thursday (and probably for other grandstands too).