Two Pokémon but you could only catch one.

I spoof like a MF. GOTTA CATCH EM ALL

unknown easy.

there is no counting on the others having a usable IV/CP/moveset but you might only get one chance to put that unknown into your dex.

So I got 4 Dragonites (one maxed at level 30 today with DT/O; the other 3 are SW/HB not maxed out to level 30), 2 Snorlax (one is legacy ZH/BS maxed at level 30; it took me FOREVER to level him up), and 1 Blissey w/ ZH/P that I'm currently walking, trying to level up. I don't have the other two. Unown I don't care too much about. So with the above info, I guess I'd want the Tyranitar because I don't have one. I only have 60 Larvitar candy.

Unown!!!

Tyranitar. Reason: I have A-rated movesets (with great IVs) for Dragonite, Snorlax, and Blissey, and I have an Unown (actually, since Unown only has one moveset, I've got an A-rated one for it as well), but my Tyranitar has Iron Tail/Fire Blast (boo!) and I really want a Bite/Stone Edge or Bite/Crunch Tyranitar.

Unown definetely

I have good enough Blissey, Snorlax, and Dragonite mons to get the job done.
I have a hatched larvitar, which in time will become a Tyranitar, that box will eventually be checked.
I have no idea if I'll ever be lucky enough to come across an Unown. Given the option, I'd have to go with the Unown.

Unown...no contest

Unown because of the rarity. The others when caught in the wild would likely only be worth a few candy and not have especially good CP and IV unless you got REALLY lucky.

Unown, because it's the rarest and I already have all others.

Well, this would never happen as nothing shows up near my house, but if it did (or if it showed up at a poke park) there is no doubt:

Unown.

Why? Rarity. Don't have a tyranitar, but hatched a larvitar and will eventually evolve it. But unown seems to be nearly as rare as articuno, lol.

Tonight (few hours ago) I dreamed I was in my hometown (very small town, with 2 pokestop & 1 gym) and some big traditional celebrations were going on, so a lot of people in the streets.

I was playing PoGo and the streets were FULL of pokemon, a lot of different semi-legendaries and even legendaries!

Firstly I encountered a Moltres, then saw Tyranitar, Lapras and I attempted to catch a shiny Dragonite with 0 CP!!!

I couldn't get 'em all because they were a lot indeed!

I was a excited and trying to put my pkmn in yellow gyms, there were a lot!

At this point of the game I would go for Snorlax or Blissey, just for the candies and the possibility of them having high CP/IV.

I won't worry at all for unown, the 26 medal badge shows that there will be an event at some point (my guess something related with legendary gen2 dogs Entei, Raikou and Suicune). In some months unown will become the new ditto, everyone will have all of them and hundreds of candies. I still remember running around catching all pidgey and rattata when ditto was released, now I have over 400 candies and it is a completely useless mon (unless you have a 90%+ IV one and you need it on the future for breeding).

But I don't think we gonna get a Snorlax/Chansey event, and if it comes it will be on Japan like the last ones or big cities on the USA, not in my small town.

The better of the list are without any doubt Blissey and Snorlax.

If I saw a metapod or a kakuna I would go for metapod because kakuna looks mean :(