[QUOTE=Chickenpants;17813756](1) What is your home airport? DEN
(2) What types of fares do you usually buy ? Economy
(3) How many miles do you usually fly each year? 100k+
(4) Do you have any kind of status at present? What is it? Premier status on UA, A-list preferred on WN (lol)
(5) What is most important to you in a FFP? Upgrades, Redemption Mileage Accrual
(6) Which routes do you fly most often: Mostly between DEN and California (DEN-SMF, DEN-SFO, DEN-OAK, DEN-SNA, etc.) occasionally outside of CA, but almost exclusively domestic.
(7) Preferred Airlines: No preference
(8) Do you travel for work or pleasure? Almost exclusively travel for work

I would go with both actually. Get the US trial preferred for instant silver and try to put as much on US as possible (you should get to chairman with 30k US miles in 90 days). That also gets you *Silver on united for slightly better treatment. I'd either pay out for the E+ option on united, or credit 25k miles to get E+ for the times you're on united.

UA will have more choices, but that doesn't help you if you get stuck on US due to company policy. Upgrades on short flights are very easy on US, and would be much more difficult on UA given the hub status of DEN.

Downside of US is that you need to walk to the end of the B concourse in DEN. US also has longer flight times for meals, which means you may get a soup/salad on UA and a snack basket on US.

No reciprical upgrades, which is why it's good to have status on both.

The mileage bonuses are the same for US/UA. US has more promos (read the Grand Slam section). US also has better redemptions to Asia. UA has one way awards, US does not. Availability is similar although UA did starnet block in the past (restrict partner availability).