Didcot Parkway has 5 platforms and has good visibility of all trains from just one platform. It has a good facilities like food and drink, shops and other amenities. Didcot is now fitted out with LED boards so easier to read all of the train times.
http://buildmate.com.sg/?product=sealer-oil-base There are lots of high speed trains that pass through Didcot; so be sure to stay away from the edge of the platform!
You can see Didcot railway museum from the station and there is a direct walk through to the museum.