It depends what you want really. If you just want somewhere to rest your weary legs/get a few minutes kip then any will do. Those along the start/finish straight will give you good views of the build up before the race, and of course the start and finish of the race itself.
Any stand opposite the pits has to have merit as you can see the goings on in the pit garages during the race. Very atmospheric in the night hours of the race in particular.
For me the ACO stand is the best of the bunch (now 2 grandstands - presumably due to the popularity). Views of the pits as stated above, also lower priced food and drink compared to the rest of the circuit, and (this is the best bit) clean and well maintained toilet and shower facilities.
In addition you can sit under the stand in the shade if it's really hot and enjoy a beer whilst checking the numerous timing screens and live footage of the race to keep an eye on what's going on on the track. Similarly if the weather is sh*t it is a great refuge.
For my money it's the best benefit of ACO membership.
