i'm in your conscience
Since you're new to them and only have that, you should start off with HeartGold or SoulSilver, I think. They're remakes of the second generation game, and although nothing beats the feeling of playing the original games, it's the closest you'll get to playing an older game. It's a good game to start with, really!
Then you should move on to Platinum. Don't touch Diamond and Pearl. The Pokedexes are rather limited, the games run slowly, and Platinum is just the better choice altogether. :)
Then go on to Black or White and after that, Black 2 or White 2. I recommend White and White 2 personally, but that's me being biased as one of my favorite Pokemon is obtainable in White and White 2, haha. Those are the latest games until X and Y. Though tbh, you could probably get away with skipping Black and White. They're good games, but with generation 6 coming in October, it'd be cheaper to just play Black 2 or White 2 and not bother with the ones before it. Platinum isn't necessary either really, but I strongly recommend at least starting with HeartGold or SoulSilver.
I hope this post made a bit of sense, but if not, just post and ask more questions, or feel free to message me! :)