My suggestion would be to do an overnight in Banff rather than Lake Louise. Lake Louise is much closer to Banff then Jasper, so you can go out from Banff for a few hours to see Lake Louise and nearby Moraine Lake. You can rent a car or do a tour by bus. There are hotels in the Lake Louise area but there aren't a lot of choices. In Banff there are lots of hotel choices in different price ranges (budget, mid-range, and luxury), and lots more restaurant choices and things to do.
You could do 2 nights Banff + 1 night Jasper or vice versa. It depends on what you are looking for. Banff is more visited and has more to do, more hotels and restaurants. Jasper is a little quieter and less produced. I have seen more wildlife (bears, mountain goats etc) in the Jasper park and near the town and I have only been there twice, but I have been to Banff probably a dozen times (I live close). I like Jasper more because it feels more like the middle of nowhere to me. :)