I have stayed at both properties many times. In August my preference would be to stay at The Banff Springs for the entrie time and make day trip to Lake Louise. The two hotels are very similar and both are lovely, but I have found (as is the case of many older hotels) the rooms are inconsistent and some are very small. Both locations are spectacular especially if you are planning to do a lot of hiking and backkpacking. IMHO the advantage Banff has is that it is located in a town so you have a lot more choices when it comes to dining, entertainment, and shopping. Chateau Lake Louise is ideal for a ski trip. Calgary is a very nice city - you may consider spending a day or two there as well.