DL Silver or CO Gold?
 

I have a friend that is currently silver on DL with 16500 MQMs and also silver on CO with 29500 EQMs. She flies DL for work a few times per year and CO for leisure travel about the same amount. With the double promo on CO she is about equal striking distance of either requaling DL silver for next year or getting CO gold.

She doesn't expect to do more than maybe 2 more LAX-NYC trips this year, so she asked me which to go for, DL Silver or CO Gold. Any suggestions?

Do both. They'll be in different alliances.
Use fare compare (depending on where she is located) to find great fares, and do the MRs.

1. CO Gold is worth 100% bonus, and upgrades are complimentary based on availability 3 days out. Double mile promo is worth it. You also get fed. CO Gold will be Star Alliance ELITE PLUS, and that is also worth it. Don't bet on fellow *A airlines doing upgrades, however - UA wants upgrade certificates and US, while giving their own elites upgrades, doesn't appear to do so for other alliance elites.

2. DL Silver is worth it for Skyteam, but will be Skyteam Elite (not Elite Plus). 25% bonus for Silver, but DL is generous on promos and MQM offers, though no double MQM promo right now (except 2-night Hilton stays thru 10/31 - use it). Advantage is that any miles over the Silver Elite threshhold will roll over to next year qualification. (none below if she doesn't make it). Complimentary upgrades based on availability 1 day out. GoGo internet codes abound.

If she really must choose, I guess I'd lean to CO, based on the extras, but it is ultimately up to her, and if she plans any international travel.

Actually the Hilton MQM offer ends 10/15, not 10/31

How about gold on CO and then status match to DL?