When to go:
I stayed in Nyaung U, the most distant of the three possible places to stay, but with just 5 km from Old Bagan still manageable. I always got up at 4:00, that leaves plenty of time to get to nearly every sunrise spot by bike before sunrise. Actually on the second day, it was even enough time to walk to Shwesandaw Paya, since, yes, I flattened both tires of my bike on the first evening - shame on me ;-) And dont forget your torch! Also for inside the pagodas, it can get really tricky to find the small narrow stairways up to the top.
Where to go:
The sun sets behind Tangyi Mountain (over the Irradwaddy behind Old Bagan) and rises in the east, from the viewpoint of Old Bagan approx. behind the airport, for orientation. So you have to choose your viewpoint depending on what you want :
- the pagodas between you and the sun, which means their black silouettes under the
- you between the sun and the pagodas, that will be lighted up in deep orange from this
And forget guidebook tips, I followed Lonely Planet to Sulamani and Mingalazedi Paya, just to find their terraces closed for visitors. One pagoda you cant go wrong with is Shwesandaw Paya -good for sunrise and sunset due to its central location. But things can change quickly here, closing or opening the terraces of pagodas. (rumours said that most pagodas get closed so that tourist have to use the watchtower - but avoid that by all means.)
For sunrise behind the pagodas my favourite one is Mee Nyein Gone Paya (=Nyein Gon Pagoda), the second pagoda on the right side down the Anawratha Rd., corner Bagan Nyaung U Rd./Old Bagan. From this terrace you have them all in one line in front of your camera.
For sunset Pyathada Paya would be my choice, since it is one of the furthest in the east with the massive pagoda field in front of it. It also offers the biggest terrace with a smaller one on top. The gate of the stairway was open during my time, though a lock could be there at anytime.
A thing that's high on the list of many travellers to Bagan, and in my opinion an absolute must, is to see a sunset over Bagan.
there are various trips organised, which will inevitably involve you ending up jostling with busloads of camera wielding tourists.
Alternatively, you can either just pick a temple yourself or get some of the locals to take you to a less frequented place. There is something quite magical about watching the sun setting over the vast expanse of the plain with it's myriad temples. It's very relaxing, almost totally silent, and the colours are amazing. Treat yourself. Be aware that there are some temples you are not allowed to climb on for conservation reasons. Notable amongst these is Minglazedi which used to be a very popular place for sunset watching.
There are other temples from where you can see the sunset, but from Shwesandaw temple it is particularly special. I went there twice.