Which of these hotels on the Las Vegas Strip should I stay in?

Why not good pools? The pools will be open then as it is the best weather in that month here. So you may consider Flamingo which has an awesome pool area. On your list I would suggest Harrahs. Forget about Stratosphere and Riviera as they are too far away from the main part of the strip. IP has a great location but unless you want to spend the least amount of money on a room then avoid them but that would be my second choice on your list.