Since I'm getting the damage buff from Psychobuff already, I use Ultrajet instead. As a character with a small AP pool, the 100 extra AP I get to burn through for free while bullet timed is great, especially as I tend to use AP greedy weaponry (heavy guns, super sledge)..
Typically I'm on Psychobuff, Jet Fuel, and the Orange Mentats mentioned previously, with Ultrajet hotkeyed for intense fights.
With both Chemist (for the 200% duration buff) and Chem Resistant (look ma, no side effects!). Started off with just Blood Cleansers in my power armor, but it worked. Only ended up addicted once early on (and then, just to Graqe Mentats due to using them to buy stuff, and I had the power armor off). Got Chem Resist 2 and all good.
I dunno. I think a 25% damage boost (with major stat boosts - Psychobuff or Psychotats) is pretty substantial. It's really noticable when I'm fighting without it and when I start buffing. When I can get it to run for 24 minutes before running out, that's a considerable amount of combat that a single dose can cover.
Heck, even Bufftats is useful. The downsides to the Psycho part of it is the major penalty of addiction. Chem Resistant is basically required unless you're willing to non min/max and suffer the penalties.
It's the raw, base chems (Buffout, Mentats, etc) that just kinda svck. Psyho and Jet are useful on their own (damage boost and bullet time), but are very, very addictive. Initially their duration is also extremely short. Mixing Psycho with Buffout or Mentats both extends its duration but boosts its overall effect. 25% additional damage while also getting a +3 Strength buff is a massive melee booster. Adding +3 to Perception greatly increases VATS accuracy with Psychotats.
TBH, the biggest drawback to chems are the companions who don't like it and make you fight without (or make their getting their affection perk really hard) after being used to them. Cait, after doing her story quest, basically got tossed into Coastal Cottage in the middle of nowhere and forgotten about. Piper, Nick, Curie all are ok with the chem use (but might snark on you for it), but dislike getting addicted. It took me like an hour to get Hancock maxed. 