I will give it a shot. Though there is a difference between a singl episode, starting to find it's footing, and being consistently good.
TOS: Immediately. On all 3 counts. I view TOS1 as the best season in the history of Trek TV. The first 3 episodes in production order (The Cage, Where No Man Has Gone Before, and The Corbomite Manuever) are all very strong. The the release order with Man Trap and then Carlie X not quite as good, but WNMHGB is still 3rd.
TAS: Immediately/Never. Not sure TAS ever was consistently good. It is my least favorite Trek show. But some of the strongest episodes were certainly early. The premiere was solid. Yesteryear is E2, and the best of the 22, IMHO. The Lorelei Signal is also a favorite of mine, and that is E4. However good it got, it got there quick.
TNG: Started to find it's footing in S2. Measure of a Man (S2, E9) was the first classic, but Elementary, Dear Data (S2, E3) was clearly better than any S1 offering. Pulaski & Data coming full circle in Peak Performance. Still, it wasn't in full bloom until S3.
DS9. S2 again. The first great episode was a little earlier than TNG, with Duet (S1, E19). But they really start to find their footing in S2 as Necessary Evil, The Maquis (2 PT), The Crossover, and The Jem'Haddar get most of the pieces on the board for the rest of the series. Full bloom maybe not until S4, and S6 is my clear favorite, but fully on its feet by S3.
VOY: Immediately, but then it got got lost and had to find its way again in S4. I thought Caretaker was pretty good and episodes like Paralax, Time and Again, Phage, Eye of the Needle, and Emnanations were strong. And Jetrel late on. Only 16 episodes. But the whole S2 Seska/Chakotay/Kazon kind of lost me, though I did like Basics, and there were some good S2-S3 eps. Towards the end of S3 it regained its footing. Distant Origin to Scorpion.
ENT: S3. While the premier was interesting and S1 had some good eps (The Andorian Incident, Shuttlepod One) and Carbon Creek (S2, E2) might be my favorite episode, I think S3 is where things found their footing. With S4 being the best and building on that S3 foundation. Twilight, Similitude, Carpenter Street, Azati Prime, E2, Countdown, Zero Hour.
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DISCO: Immediately. DISCO's issue, for me, wasn't finding its footing, it was staying on its feet. For me, S1, S2, & S3 all started strongly and ended badly/stupidly. S4 finally stuck the landing but started off worse than the others. For me, the premiere was good, Context is For Kings, Choose Your Pain, Magic To Make The Sanest Man Go Mad, and Into The Forest I Go remain some of my favorite eps and pre-Mirror U S1 is my favorite half season of Disco.
ST: E2, Calypso. Fantastic. Some other good ones, too: Q&A, Escape Artist, Children of Mars.
PIC: Immediately/S3. I thought PIC started off strong in S1 but did not stick the landing. Had a good start to S2 & kinda fell apart before a good finish. S3 was the only season with the full package. But Remembrance, Absolute Candor, and Nepenthe were all excellent. And Impossible Box & Stardust City Rag (if you can get over a bit of over the top ridiculousness at times) were also good.
LD: Back half of S1. Veritas, Crisis Point, No Small Parts were full bloom. LD always nailed the endings. There were hints earlier (Envoys, Much Ado About Boimler).
PRO: Early pary of S1. It is blooming by "Time Amok" (E8), but I would say Dream Catcher>Terror Firma & Kobayashi (E4-E6) is where feet were found.
SNW: Immediately.