My advice is to seek out people who really care about tomato flavor, and I don't know anyone who cares about it more than tomato gardeners (many of them grow with flavor as their top priority). There are lots of online tomato communities, but tomatojunction.com is the one I would recommend.
I also recommend a number of things when growing the tomatoes for improved flavor:
- Warm the soil (such as with black plastic, or whatever other method you like); this seems to improve the concentration of sugars/acids in many (not all) kinds of tomatoes
- Add nutrients to the soil; they can impact the flavor; a lot of people (including me) think Epsom salt impacts the flavor.
- I think fertilizing with foliar sprays helps the flavor, too (foliar sprays are said to increase the nutrients in fruits compared to ground fertilization; so, that would probably make a flavor difference).
- Soil. Different soils produce different flavors.
- Sunlight: insufficient sunlight can lessen the flavor at times
- Season: tomatoes taste different when they ripen at different times of the year
- Vine-ripened tomatoes usually taste the best, in my opinion
- Many people think tomatoes taste better if you don't refrigerate them.
- Dry-farming (many people think this increases the flavor)
Variety makes a big difference, of course. There are maybe 20k+ kinds of tomatoes out there, and there are a lot of different flavors. Most people I meet on gardening forums prefer the flavors of big pink beefsteaks, such as Stump of the World and Aunt Ginny's Purple (which is actually dark pink), for example--not particularly for sauce, but if you ask, they generally recommend such for sauce, too (flavor-wise). They also often like oxhearts, which are often a lot like paste tomatoes, with more flavor (they're meaty with few seeds). Some people like the taste of lots of kinds of tomatoes mixed together.
Some tomatoes taste better cooked than others. I think Peaceful Valley's Beefsteak is excellent cooked. I think Early Girl F1 makes a nice spaghetti sauce (but they've improved the variety since I've had it as a spaghetti sauce--so it might not taste the same).
As far as paste tomatoes go, though, if you want those, I recommend just growing a bunch of kinds to see what you like. Most paste tomatoes I've tried are kind of normal-tasting. I've read good reviews about the flavor of orange paste tomatoes, though (e.g. Orange Banana); I plan to try some next year.
If you're worried about the higher water content of big pink beefsteaks, and such, there are plenty of methods to thicken the sauce. Remember that sauce and paste aren't the same thing, though; you don't always need or want tomato paste. Tomato paste is quite a bit thicker than jam (it doesn't flow at all). You wouldn't dip breadsticks in tomato paste, normally, I imagine. One trick to thicken sauce is to add oil and a little ground mustard (or another emulsifier). The carotenoids that color the tomatoes also mix with the oil. You wouldn't want to add oil if you're canning the sauce, however (due to botulism risk with oil).
Be sure to add plenty of black pepper. It really brings out the flavor of tomatoes, raw or cooked (much as it helps strawberries taste even sweeter). I think adding paprika also helps add some extra zest. I like to add brown sugar or raisins (blended up) to my sauce if it isn't sweet enough; I think brown sugar helps thicken the sauce, too. My typical spaghetti sauce includes ingredients like these:
- Pink salt
- Black pepper
- Fresh sage leaves (blended into the sauce)
- Onion powder
- Sometimes celery (it adds a nice flavor)
Add these things when it's nearly done (if they're over-cooked, it's not as good):
- Extra virgin olive oil
Chives are really nice cooked into spaghetti sauce, too.