UA 1MM is lifetime Gold, 2MM Plat, 3MM 1K, 4MM GS. US 1MM is lifetime Silver, anything above is Silver. If you think you'll be flying enough to be >1MM, lifetime Gold is >>> liftime Silver.

I switched from US to UA in 2007 after I reached 1MM and got absolutely nothing (before US impemented lifetime Silver benefit), after having been a CP and equivalent for ~10 years. I requested and received a status challenge to 1P (now Gold) and was able to get 100% RDM bonus while I made my way up to 1K.

I recommend rerquesting status match/challenge from UA, and use the potential merger of US/AA as justification for UA to grant request. Then you will not lose much bonus RDM while you work up to 1K.

I have been very happy with UA, even with the post merger fiasco.