What should I look for when choosing tomatoes for pasta sauces?

From a production standpoint, you might actually be better off asking this question on the gardening site.

In general, however, for canning purposes you'll want to select a 'determinate' variety -- they tend to have all of their fruit ripen around the same time, rather than having it be spread out across many weeks. Indeterminate tend to be better for tomatoes that you might want to use for salads or other purposes, as you won't suddenly be stuck with a glut of tomatoes that you can't use all of.

Your other gardening considerations are if the plant is more bush-like, or more vine-like, as it'll affect how much you need to do to manage them. The vine ones you have to keep checking them every couple of days to make sure the vines are fed back through the tomato cages so they don't start drooping against the ground when they're laden with fruit.

In general, you're going to want to select a plum-style tomato. Sometimes they also label tomatoes as 'sauce' or 'paste' tomatoes. Other varieties of tomatoes tend to be a bit more wet and can require more cooking down, although other varieties may have some advantages.

As for the specific variety, San Marzano and Roma are two well known varieties, but there are now a large number of hybrids that I'm just not familiar with. I would personally select for varieties that do well in your local climate, and can deal with the specifics of your garden (eg, how much space you have to work with) ... but again, ask that on the gardening site.

In the article that I linked to above, they actually recommend blending multiple varieties, but this is more difficult in a home garden unless they all ripen at the same time. You could always plan for the bulk to come from a determinate variety, and blend in some from one or more indeterminate varieties, or plant a couple of determinate varieties, or stagger them some to try to get batch sizes that will be easier to deal with.

San Marzano and Viva Italia make very tasty sauces if you grow your own, and boil down the seed-strained mash using only the ripe fruit. It doesn't take many green ones to make the taste too sharp.