The Docklands are rather East. The Chelsea ground is very West, and a long (boring) trip from the Excel. Apart from that, there are excellent transport links from East to Central, so the main tourist sights are well served from that area but you might be better off looking at West London.
The Premier Inn is between Custom House DLR and City Airport DLR stations. Whilst not the most central of locations you can walk to either DLR station and commute in. The new cable ride across the river (which is fab!) will get you to North Greenwich Jubilee line as well as the O2. So really it depends on how much you are prepared to travel into town before you start your sightseeing trip, I actually live further East than Excel area and quite often use the trip in planning/reading about what we are going to see. Hope that helps.