As a BWI flyer, my main carriers have been UA and CO,with WN for short hops or nonstops when necessary.

I use UA almost exclusively for international travel.CO will be joining Star Alliance in October,giving more options.

I tend to use the SPG AMEX for most things,but I also carry a UA card and a WN Visa,which I use to boost credits to get a CP. Unlike you,I am in hotels often,so I also use their cards also,especially when there are bonuses available.

If you decide to go with UA,the conversion from SPG is not good,which is why I keep a UA card in case I need to boost points.I earn most of my UA miles BIS,which sounds as if it is not the case with you.

I have had good luck redeeming rewards on UA also,especially if you can book early,keeping in mind that schedules seem to change often.I just had my 5th major schedule change on a September 09 trip on UA.

If you fly enough to achieve status on UA,you are also entitled to E+ access,which makes UA stand above all other coach products for me,especially internationally.

I'd charge only enough on the WN Visa to maintain your CP then switch to whatever carrier/card you decide upon.