I think the best strings would be ... eh ... free!
I hop around from brand to brand. DRs are good and last longer than most IMO but they cost more. The Ernie Ball purple slinkies (with the lower end bass strings and 11s for the high E, I think ? wow are these great with a detuned Strat) have a great fat tone for Les Pauls, but I'm trying to stick to 9s or 10s to prevent another tendonitis incident, at least 9s on the Strats I play every day. Even the cheapy D?Addarios are basically OK. I think Ernie Ball Slinkies tend to discolor my fingertips more than most after awhile. I don't see a colossal difference in any brand in the 9-10 range. I've used Fenders on Gibsons and vice-versa. For jazz stuff on 11s I?ve enjoyed the DRs and the Thomastic-Infelds.
I buy strings at the local shop if they aren't too outrageous, because strings have a high gross margin and that's partly how they can stay in business, because they really don't move that many guitars or basses or amps. It's like film pays the bills at a camera shop. I think buying mega-cheap strings at some of the bigger Web sellers is bad overall, because it eventually hurts the little guys, and I want the little guys to stay around. The local Fender dealer just boarded up his place, and that is sad. I have bought a case or two of strings online in the past, but I try to spend it locally.
I think that given the overall decent quality of most major brand strings, that guitar picks can make more of a tonal difference. I use Dunlop Big Stubbies (3.0 mm thick) and while they take some getting used to, can produce a really fat tone, and the pinch harmonics are decent, too. The Pickboy CelTex heavies have better harmonics, but the Dunlops are fatter. They are rigid, totally inflexible. For the ultimate fat sound I use the edge of the pick - it's like a purple rock. They also make a triangle Big Stubby, but that seems like a drink coaster to me. Sound good, though.
While I'm rattling on (and off the topic, actually, as I usually do wander :roll
I sometimes find some interesting pick-shaped tumbled stones at the local rock and mineral show that work well as picks. I've even used bits of clam shells when I lived in coastal New Jersey. I know someone who uses picks made out of old piano keys. I usually play with the Dunlop and two fingers. But I also play with just my fingers for some single-line stuff - I believe that gives the best overall control of the strings, although it beats up your skin. Clarence Gatemouth Brown just uses his fingers and that old guy can really fly around the fretboard!