If you are doing primarily domestic travel, then my view is that you should split loyalties after 50K miles if you know you will be flying another airline at sometime during the year, unless of course you are shooting for lifetime million miler status. The top level of any FF program (UA 1K, US Chairmans, AA Exec Platinum, CO Platinum, etc.) is very overrated in my view. Upgrade success at the 2nd tier is almost the same as at the top level and I believe with the exception of CO, the bonus mile % is the same.