Picking between Red and Blue decides which Pokemon you can catch on your own and which ones you need a trade for. Here's the Pokemon Red vs Blue difference in one sentence: each game has 11 wild Pokemon the other one doesn't, and almost everything else is the same. Those Pokemon are the Pokemon Red Blue exclusives, and you'll want to know them before you buy, because whichever ones you miss take a trade to get.
The rest of Kanto doesn't change. You start with Bulbasaur, Charmander or Squirtle either way, you fight the same trainers and you meet the same legendary birds. So the choice comes down to a short list of Pokemon, plus a handful of prizes at the Celadon Game Corner.
Which wild Pokemon only one version has
Red is the version for Growlithe and Arcanine, Mankey and Primeape, and the line of Oddish, Gloom and Vileplume. It also has Ekans and Arbok, and it's the only one where you can catch Scyther and Electabuzz in the wild.
Blue pairs off against that nicely. It has Vulpix and Ninetales where Red has Growlithe, and Bellsprout, Weepinbell and Victreebel where Red has the Oddish line. It adds Sandshrew and Sandslash, Meowth and Persian, and the two big ones, Pinsir and Magmar. (Pinsir has pincers and a bad attitude.)
| Only in Red | Only in Blue |
|---|---|
| Ekans | Sandshrew |
| Arbok | Sandslash |
| Oddish | Vulpix |
| Gloom | Ninetales |
| Vileplume | Meowth |
| Mankey | Persian |
| Primeape | Bellsprout |
| Growlithe | Weepinbell |
| Arcanine | Victreebel |
| Scyther | Magmar |
| Electabuzz | Pinsir |
Neither side is longer than the other. It's 11 against 11, and the best way to choose is to look for the Pokemon you'd want on your team.
The Celadon Game Corner prizes differ
The prize counter is the other place the versions split. Red sells a level 25 Scyther for 5,500 coins, and Blue sells a level 20 Pinsir for 2,500 coins, so the big prize costs less than half as much in Blue and arrives five levels lower. The Nidoran line splits too: Red sells a level 17 Nidorina and Blue sells a level 17 Nidorino, both for 1,200 coins.
Even the shared prizes aren't the same. Abra is level 9 for 180 coins in Red and level 6 for 120 coins in Blue, and Clefairy is level 8 for 500 coins in Red against level 12 for 750 coins in Blue. Dratini is cheaper in Red, a level 18 for 2,800 coins against a level 24 for 4,600 coins in Blue, while Porygon flips the other way: Red asks 9,999 coins for a level 26 and Blue asks 6,500 coins for a level 18.
Brock, Misty and the rest are identical
Brock opens the Gym route in Pewter City with Geodude at level 12 and Onix at level 14, and Misty is second in Cerulean City with Staryu at level 18 and Starmie at level 21. Lt. Surge follows in Vermilion City, and his team is the same too. The data for the two games matches on every trainer, trade, shop and item, so a strategy that works in one works in the other.
The legendary Pokemon match as well. Mewtwo, Zapdos, Articuno and Moltres are in both games, and so are the fossils, Eevee and Lapras. All that changes is the list of wild Pokemon and the prize counter.
Which version should you pick?
If you want Arcanine, Scyther or Electabuzz without a trade, pick Red. If you'd rather have Ninetales, Persian, Pinsir or Magmar, pick Blue. For a first playthrough it barely matters, since the Gyms, the story and the starters don't change, and whatever you miss takes a single trade to fix.
Prices might tip you if you plan to spend coins. Blue's Pinsir and Porygon cost far less than Red's Scyther and Porygon, while Red sells Dratini for 2,800 coins against Blue's 4,600.