New to FlyerTalk, new to the FF miles game...

Over the years, I've accrued between 30K and 40K miles in each of my DM and Delta SM accounts. I'm going to use up those miles for some travel I'm planning in the future. However, from now on I want to concentrate on only one of the accounts.

I fly maybe 5 times a year from PHL on US Airways (they are generally the cheapest to places like LAS and BOS from PHL). So, I accrue very little in terms of actual "preferred" miles -- and thus I'm not interested in the elite/chairman level programs.

I have both the new US Airways MC and the AMEX Skymiles Gold cards. I've been using the MC to book my recent trips on US Airways (3x miles). I also stay at the Marriot half a dozen times a year and have my Marriot Rewards linked to my DM account. In addition, I have about 25K in AMEX membership rewards points, that I could transfer. The issue is...that DM no longer participates in MR -- and thus my only choice is to transfer to SM.

My question...moving forward which account should I stick to? Will the merger with American West make the DM program better? I'm mostly interested in seat availability for award purchases (from my own research, I've seen complaints about limited seats on Delta)

Thanks