I think for the most part, we're splitting hairs here. CO's domestic fleet is pretty consistent with respect to the first class cabin. The notable exception would be a 757-200 with international BusinessFirst seats, which does serve the LAS-EWR route occasionally. But as mentioned, the LAS schedule seems to change quite frequently.

I would choose my flights by schedule first in this case (unless a 752 shows up, then sometimes I'll make a sacrifice).

That being said, I agree 1AB on a 753 are probably the best seats, and the door 2L boarding on the 753 creates a more tranquil boarding experience. (It also means you usually have to fight with coach pax when getting off the plane unless the FAs block them, which they sometimes do.)

But a drawback of the 753 is the 24 seats served by 2 FAs which makes service incrementally slower and less personal than the 16-20 passenger cabins on the 737s (also served by 2 FAs).

If you can get a plane with DirectTV / inseat power, that would probably also be a factor. It's probably difficult to guarantee that well in advance, but a First Class ticket is flexible, so you may be able to change flights a day before when the IFE details are posted on pda.continental.com.