I do agree with the idea of focusing most of your mileage accrual on one carrier, but don't "discontinue" your FF account on the other, either. You never know when those miles or that account will come in handy. I accrue the bulk of my miles on BA (and am Gold as a result), but I still use my accounts at DL, UA, AA, etc. on a regular basis. My frequent international travel often ends up being on a random assortment of overseas carriers that might belong to any of the big alliances, so I end up racking up miles in my smaller accounts too. Between the earned miles and transfers from CC accounts etc., I've gotten an awful lot of award trips out of them.