Just my opinion and experience, which hold less water than an old Campy aero bottle:

-Best price, generally 2x8 RSX STI, because they're a bit lower grade and generally were sold as part of a "package" bike by big-box-bike shops.
(Do not confuse them with the much nicer 2x7 RSX STI)

-Best value, generally, 2x8 Shimano 1056 (105 in the greenish-gray), because they work well, can be rebuilt, hoods are out there, and can be cheaply found.
-My preference, generally, 2x8 Shimano 600/Ultegra. Nicely done, smooth as silk, but come at a higher price.
-Often overlooked are RX100 STI's, which I've never seen but have heard of, similar to the 1056 but polished, not anodized.
I think all of these share the same hoods, which explains availability, and they work with each other's RD's.

There there is 8-sp DA, which you are supposed to pair with a matching RD. Neither the RD nor the shifters play nice with the non-DA stuff.
Hoods are close to non-existent, or very expensive from the hoarding speculators.

Then, there are the new Sora and Claris. Depending on the type of riding you do, these can be the best situation. The Claris tend to break a bit.
The Sora take advantage of trickle-down technology, and are generally for riding the hoods due to a poorly placed thumb button.

Also, you may want to look into Microshift's 8-sp models. In my opinion, superior to Sora and Claris, and compatible with Shimano.

Depending on the quality of the bike, the availability of an RD, your budget and riding habits, I'd go with used 105's, used 600/Ultegra's,
and if not, Microshift. Bear in mind many Shimano 7-sp RD's will work with the 8-sp STI shifters. Some will not.

Much luck to you, ask any question you want, and Welcome to our own little den of iniquity.