Suggestion?

[ChaosYoshi]

I'm going to take each of your requirements and give my honest opinion on the best.

•have no crappy graphics

I'm assuming you mean how pixelated the animations look in Black, White, Black 2 and White 2 (or the Gameboy and Gameboy Color games which is to be expected because of age). In that case, I would say that while a lot of the Heart Gold and Soul Silver battle aesthetics are mostly unchanged from Diamond, Pearl, and Platinum, the overworld looks a lot better in my opinion. That is until the jump to the 3DS, obviously since it's on a stronger system. The overall aesthetics look great on the system, though the 3D effect is not that appealing to me. Just remember that a game is not bad only because it has bad graphics, so I'm hoping this is not a huge deciding factor for you.

•good storyline

Pokémon Mystery Dungeon: Explorers of Time/Darkness/Sky. In terms of the mainstream games, I would highly agree that Pokémon Black/White & Black 2/White 2 have the best stories by far. Pokémon games are not really known for their stories, but I think these do a good enough job.

•great battle system

The thing about the Pokémon games is that as more games are released, the more polished the battle system gets, so the latest ones get the award here.

•lots of things to explore

Pokémon games tend to have a lot to do, even after you reach the credits. The ones that I find that have the most replayability are Heart Gold/Soul Silver and Black 2/White 2, especially the later with the Pokémon World Tournament.

I hope this has helped you in some way.

[Dtroid]

I'm going to take each of your requirements and give my honest opinion on the best.

•have no crappy graphics

I'm assuming you mean how pixelated the animations look in Black, White, Black 2 and White 2 (or the Gameboy and Gameboy Color games which is to be expected because of age). In that case, I would say that while a lot of the Heart Gold and Soul Silver battle aesthetics are mostly unchanged from Diamond, Pearl, and Platinum, the overworld looks a lot better in my opinion. That is until the jump to the 3DS, obviously since it's on a stronger system. The overall aesthetics look great on the system, though the 3D effect is not that appealing to me. Just remember that a game is not bad only because it has bad graphics, so I'm hoping this is not a huge deciding factor for you.

What I mean by "no crappy graphics" is that it have no:

• obvious pixelated things (though,if only some is pixelated,I'm also okay with that)
• no bland colors

[UsuarioTHf]

I'll agree with Tsu. HeartGold and SoulSilver are simply amazing, and they're a great starting point.

• have no crappy graphics

They all have nice graphics. It's nothing too mind-blowing, but the simplicity of the graphics is charming. The Pokémon sprites are pretty, and they've made some significant changes during the generation shifts. For example, HeartGold/SoulSilver have the Pokémon sprites standing still in the battle, while in Black(2)/White(2) these sprites actually move in the middle of battle. X/Y are the most significant, thanks to the shift from sprites to 3D models which, in my opinion, adds a new level of depth to the game.
But it's not exactly an important factor, so you shouldn't really be focusing too much on this.

• good storyline

As CY said, Black/White and Black2/White2 have the best storylines, only because they don't have your typical "hurrdurr we'll do evil stuff stuff to screw up the world" storylines. Personally, I felt Black/White were really slow gameplay-wise but they're important if you want to understand Black2/White2's stories.

• great battle system

Uh, all right. This is kind of a weird one.
As CY said, the creators try to polish the battle system after each generation. Perhaps the switch from Gen 5 (Black[2]/White[2]) to Gen 6 (X/Y) was the most significant, adding a new type (Fairy) as an attempt to counter one of the most powerful types in the games (Dragon) and as an attempt to buff some previously unused offensive types. They also added a bunch of minor changes that are sort of important.
So X/Y will be sort of different from the rest. But they're all good.

• lots of things to explore

HeartGold/SoulSilver. You can explore two regions in the same game, effectively mixing two games into one. Besides, there are also many fun minigames and post-game activities such as the Pokéathlon and the Battle Frontier which make the fun of the game last even longer.

[ChaosYoshi]

Reading back on what I said, I think I should state that it's more of the 3D feature of the 3DS that doesn't impress me. The fact that the game is using 3D models is fine.

[Raz]

Most people who use the 3ds do not use the 3D feature anyways. The games on the 3DS never require it. The 3ds is the best (yes, I can say this without any regrets or denial) handheld and should buy it for more than just X/Y