If you only have two nights to spare, should you stay in Grasmere or Ambleside??? ( both located in the Lake District(
They're not very far apart. Grasmere is probably the prettier of the two, but if you're using one or other as a base for that part of the Lakes rather than a place to stay in themselves, either will do. If you stay in Ambleside, I'd recommend the Apple Pie b&b. Either is fine as a base for walking, though Ambleside is closer to Landsdale (I think the best way to go up Scafell Pike).
Both are overrun with tourists (when driving through Grasmere last October, I had to crawl at 5 mph as the pavements were not wide enough to cope with the number of day trippers so they were in the road), but I think that it is nicer than Ambleside.