DL or CO...CO HANDS DOWN
 

I live in Atlanta and have been with both for many years. when they were aligned I would up on CO to hawaii 90% of the time even if I used delta miles...CO has much better flights going west...DL is better to the islands as CO makes you fly to newark, houston, or even Minneapolis to get there...I hate flying north to go south....right before the split I used my last DL miles to get a great CO flight to cancun...they even beat DL to there. With the new award teir system all the cheap flights are 2 connections, red eyes, or unavailable...what a favor they did us when they spun the new system as being better for the consumer....LMAO
Delta also has pityful customer service...after waiting in line for 30 minutes at the broken kiosks and another 30 to get to the counter we were 3 minutes late checking bags in Vegas....nothing they could do for us but charge us more money...I told them then they were too greedy and they can go bankrupt for all i care....using the last of my wifes skymiles end of the month for MBJ after that DL can kiss it....I now have over 100k in CO and can get another 50 through chase, and 45-60 on UA with offers...looks like star alliance is my new best friend....ATL-HNL or OGG are some of our favorite awards and availabilty is awesome on CO.

CO is not exactly 'quite generous' on LH and LX metal flights. For LH, discounted economy class will only earn you 50% EQM. UA MP will give you 100% EQM in those same classes (W, S, and U). And for LX, there are no bonus miles.

Regarding bonus miles, Skyteam is more generous when flying partner airlines.

Do you know specifically when?

A reasonable price and easiness to redeem miles on international coach tickets is the most important decision-influencing factor for me to choose my airline. Ever since my first flight with NW, I have never been upset about my choice until the day when www.nwa.com disappears.

I am in the middle of switching to CO at this moment. This year I have two more paid trips with DL and all the remaining paid flights will be on CO.

It is not an easy decison for me to make, as I have a large balance of SM with DL and that I know it would be impossible to redeem them at a reasonable price once I lose Platinum status after February 2012. However, recent experience redeeming miles (including the airline's own award availability as well as parnters', website function, agents' knowledge and willingness to help) with CO and DL is such a striking difference that triggers my final decision -- I am waving my hands to DL (or it should really be ex-NW) and heading back to the CO camp. I have always been longing for those old moments in DTW, MSP, IAH and EWR when CO and NW were the best partners. Now the time is coming again.

What I might miss on DL -- easy upgrade even on transcontinental flights like JFK-SEA, SFO-JFK. However, since I do not pay for those first class or business class tickets, I will not feel disappointed if I do not get upgraded. I view it as the airline's courtesy to the elite members.

Just my two cents.