I'm with Roadrunner on this. Whereas he has kids to think of I, like many, try to get a seat where somebody won't stand in front of me. At Stamford Bridge an Upper Tier front row seat is ideal but I bet there will be a few 'standers' looking to buy seats in that row. It was the same at Everton...
I got in early and bought a front row seat in the upper tier. It's not the worst away end but it isn't anywhere near the best either. I couldn't take a chance on ending up somewhere near the back of the lower sections - I would imagine the upper tier restricts much of the view