Delta offers a PMU for their platinums (top tier). It is an international upgrade certificate but it requires a Y/B/M fare, which are the three most expensive, and is capacity controlled. Continental does not offer any SWU-type instrument and there is no indication that one will be forthcoming in the near future.

Upgrades are easier on DL based on most accounts, but I was ~90% out of EWR last year (mostly on EWR-MCO/TPA/DAB/JAX runs) on CO. It depends a lot on your routes and travel times.

If you are actually going to be flying on both carriers then also consider the 50% EQM/MQM issues. Both carriers only give 50% EQM/MQMs for the lowest fare on the other. CO also has 50% earning for NW flights on cheap fares; DL earns 100% on all NW fares.

DL is a miles-based qualification only, not points/segments. This extends to CO credit on DL metal where you'll only get miles, not points (and potentially only 50% miles as noted above).

CO does have more seats available for BusinessFirst rewards for their elites, but that doesn't mean that there are a lot of them. I don't know if DL has a similar offering.

DL has also just reduced the availability of their 2x miles reward seats, or at least that was the case a couple weeks ago; I haven't followed up on it since I got back from vacation yesterday.

The other option would be to get NW elite. Same upgrades (or lack thereof) on CO metal but no 50% EQM earning on DL. Of course they do have 50% EQM earning on CO cheap fares so that may not help as much.

I think that in your case DL makes more sense if you are going to fly them more out of LGA/JFK, where they have a ton more options.

S.