(I want to start out by stating this isn't a guide, this is a question and I know little will answer it because this community is small, but hey, always have room for growth)
So I know the timing is off, but the next campaign event will be when I get the Event Campaign Reward. I have a Temporal Recruit, which is who I'm getting this for, and I am getting a Constitution-class vessel. I'm leaning towards the Temporal Light Cruiser but am a bit tempted by the MW FDC (Also, if anyone wants to comment on how good their equivalents are, I would be happy to replace a Constitution-class with a (captured) D7 or T'Liss.)
Constitution Miracle Worker Flight Deck Carrier: Has the best performance apparently. Also looks good, but the TOS one is a bit better. Also am a bit tempted by the D7...
Constitution Temporal Light Cruiser: The OG, Captain Kirk's Enterprise (also can equip TMP Skin, so yay). Looks great, and has good performance. Leaning towards this, although the MW FDC is starting to lean on me.
Constitution Mirror Warship: Not really enthusiastic about this, but I included the other ones so why not. Apparently has a really good trait but isn't full spec, which is a bit pathetic, considering its age.
(NOTE: I have no interest in buying the 10th Anniversary Pack. The only bundle I'm slightly interested in are the T6 Romulan Bundles (The Legendary Ones) and the Legendary Mirror Bundle.)
FWIW, my TOS character flies an Atlas (mainly because the Event Campaign wasn't a thing yet, and a lockbox ship was more accessible than a promo ship).
You could also consider a Paladin, Nautilus, Sagittarius, or Theseus (with appropriate TOS skin).
As far as an actual TOS Constitution-class goes, the Temporal Light Cruiser is your only choice of the three listed because both the MW FDC and the Mirror Warship are from Discovery.
Thanks for your feedback! I've considered the C-Store ships, none of them really appeal to me. I think I'll do the Temporal Light Cruiser, because it is not that big a difference if I go for the Light Cruiser instead of the FDC.
Understandable. Honestly, if I had been in a position to make your choice I probably would've gone for the Temporal Light Cruiser too. (I mean, the Atlas maybe has more deeps, but the Connie's a Connie....)
I forgot to mention it before, but one of my other characters is a TOS-styled Klingon (I wish that was a real separate subfaction, but that's a different discussion) who flies a D7 Temporal Battlecruiser. It doesn't "feel" as powerful as my other character's Atlas, but that could be down to the fact that the Klingon is a newer/lower-priority alt with less optimization and/or other differences in the build, not necessarily the differences between the ships themselves.
Speaking of which...
The D7 is IMO a straight upgrade from the Connie with the addition of the cloak, although I guess YMMV depending on how you feel about replacing the universal/command seat with universal/intelligence. However, it's not a Connie, so I'd say skip it for space barbie reasons, unless used on a KDF character after the TOS FED one has already been squared away.
The T'Liss is even more mechanically interesting, since it's got singularity core abilities (but no cruiser commands), an experimental weapon (while keeping the 5 forward-facing slots!), and adjusts the seating to have cmdr tactical/temporal instead of cmdr engineering/temporal (which is a double-edged sword because you gain the possibility of CSV/CRF III, but are stuck with 3 eng-only slots where you could've loaded up with temporal abilities before) and universal/pilot. That's all pretty neat, but again it's still not a Connie, so I'd say save it for a Romulan alt later.