How much do you want to be spoiled then?
I've already pre-ordered X. I like the concept for Xerneas so much more than I do for Yveltal (Life vs. Death). Yveltal is cool though. I don't have much of a set pattern for the series.
I had Red to start, and I don't remember a particular reason for that. My sister got Blue.
We both got Yellow, I think.
I got Gold, she got Silver. I picked Gold because she preferred Silver.
Skipped the third gen, but I got Emerald after gen IV came out (I think I made it to Victory Road and then got lazy and stopped).
I got Pearl, sister got Diamond. Again, her choice.
I got Soul Silver because I had Gold before.
Black, sister got White.
Black 2, because I had Black.
I guess my pattern is "the one my sister doesn't prefer." I don't think she has plans for gen VI though; I don't think she even finished White.
As far as starters go, I think they are all alright. Chespin was my favourite first stage and I'm still a little torn on his last stage. It's growing on me. But there is another leaked grass type that I really like and I want to see what it evolves into.
From the leaks, it seems like there aren't that many brand new pokemon until somewhat late in the game. If you haven't played since Gen II, are you familiar with pokemon since then?
On dual mega evolutions:
It's pretty much confirmed that Charizard is the only Kanto to get two. There are X and Y versions of Charizard's stone, but the others are not labelled that way.The grass type I'm interested in is
a Grass/Ghost pumpkin-bat that probably has an evolution.
I'm also intrigued by
the Steel/Fairy Klefki, a keyring pokemon that presumably steals keys. I think it is adorable.
One of the newer leaks is
a dragon type named Goomy that evolves at least once (into Sliggoo) and quite possibly twice. Lots of speculation that it is this generation's pseudo-legendary, and although it learns many water type moves and has Hydration, there are also many hoping that it becomes the first Dragon/Poison type.
Image here.
Finally, there is a bizarre
Water/Rock type named Barbaracle. It is so weird that I go from hating it back to loving it.