You really shouldn't worry about which one to play. All the games are designed to be enjoyed, by first timers. The harder mechanics in the game aren't required to understand. They're there for long fans. Pokemon Go is so simple, you don't even need to play any of the old games. That's the main point of it. If you really want to play the old ones, buy the remakes. If you can't enjoy Gameboy graphics anymore.

HeartGold is great because of all the legendaries, great layout and graphics. Downside is the steep grind endgame.

Thanks for everyone's reply especially the guy who posted screenshots, that helped a lot. I wasn't aware there were remakes, so Ill definitely start with FireRed first and then Heartgolf.

What are the main differences between two versions?
Do pokemon gamers typically buy both, or one or the other?
And how do you choose which version?

RED is my favourite

My Recommendations:

First, don't worry too much about playing the games in order. Pokemon games are only slightly more closely connected than Final Fantasy games, with each game providing all necessary info for newcomers.

Recommended

• Red/Blue - The earliest games in the series, but they've held up pretty well. The gameplay is a bit unbalanced or archaic at points, but not nearly to the extent of, say, NES RPG's. This version also uses the same group of Pokemon as Pokemon Go, and is also on the 3DS Virtual Console.
• FireRed/LeafGreen - Vastly improved remakes of Red/Blue, not just in graphics but also in interface, gameplay. I'd recommend this one over Red/Blue except that it is less convenient to find and play nowadays, since Red/Blue sold so well and had a Virtual Console release.
• HeartGold/SoulSilver - The remakes of the Game Boy Color games. a lot of people love this generation, and it has to be commended for its interesting environment and loads of content. That said, it has become one of the most expensive games in the series, costing more now than it did at launch.
• 3DS entries - Solidly made games that are very user friendly. I'd recommend them to most RPG players with a 3DS. XY and the Gen 3 remakes each have their pros and cons, but a lot of that is based on taste.

Discouraged

• Yellow - Though mostly the same as Red/Blue, Yellow had a few changes to appease fans of the anime. For newcomers though, the changes mostly make the game unnecessarily harder and have less varied random encounters.
• Diamond/Pearl - Though not terrible games, they start off slowly and have somewhat cumbersome environments to traverse. Platinum is better, but is too hard for beginners.
• Black/White - Not newbie unfriendly, and honestly rather good, but these are best experienced after playing other games in the series. Its distinct rosters of species and storyline are a bit out there for this series.

HeartGold/SoulSilver is my favorite, but X/Y are the most beginner friendly.

There is very little difference betwen versions of the same Gen. The biggest one being which pokemon you can catch. These games were meant for trading, so you cannot catch every Pokemon on one cartrige unless you trade. Sometimes there has been a third pokemon version with various improvements. Like Yellow in Gen 1 which added a bit of color a few other minor things over Red/Blue. The only time in wich a third version was far superior was Gen3 Ruby/Saphire and Esmerald, but thats because Esmerald is the least bad(harharhar).

Think of each version of the same Gen as having a few "exclusive" Pokemons each. As an Example, if I were choosing between Firered and Leafgreen I would choose Leafgreen because one of it's "exclusive" Pokemon is Staryu which evolves into my favorite Water/Psychic Pokemon, Starmie.

Firered owners will need to trade if they want this Pokemon but...

Firered, on the other hand, gets the very popular Psyduck as one of its exclusive Pokemon.

Choose Wisely

Since you're gona play Fire Red PICK EMERALD OVER THE THIRD GEN REMAKES !

I think after 1st and 2nd gen Pokemon went downhill quickly. That's coming from one of the biggest Pokemon fans growing up. I still have my collection of over 3000 Pokemon cards and 200+ Pokemon toys xD

I just felt as Pokemon went on it lost alot of it's charm.

All of them are really good, but my favorite is 3rd gen (Ruby, Sapphire and Emerald) including the remakes. So Omega Ruby or Alpha Sapphire would be my suggestion. Otherwise, X and Y are pretty good. I love 4, (diamond, Pearl and platinum) but if you are gonna play that gen, play Platinum. The battle system is so slow in Diamond and Pearl.

Gen 5 (Black/White and B2/W2) are the best in terms of story. Especially the second.

I personally am not a huge fan of gen 1 or 2. But I prefer 2 over 1.