Sad to say - free games.  Lots of them. And a lot cheaper hardware price too.

Don't see any point in paying for a portable gaming device (and then paying $$ for all the games) as what's available for free on my Android phone is plenty good enough already.

For me; that they weren't handheld...

3DS: They'd need to remove this goddamn region-lock. Or: Homebrew with some kind of Zelda-OoT3D edition (Like the GBA SP, but BETTER). After all, I want to import the games and want to be able to play them if a game wouldn't be released here (Or in a state I'm not interested in)
And if they don't remove this f****** region-lock and if there won't be some kind of homebrew, I want all RPGs that are going to be released in Japan here in Europe too (with japanese voice-acting). Sadly, that's even more unrealistic.

NGP: Dunno. It should be definitely cheap at the very least. 250€ for the 3DS is expensive enough and I don't want to spend more money on a handheld.

NGP: Sony first party support

3DS: Sony first party support, or a really really really cheap price. I'm still waiting for the DS to hit a price at what i think its worth

No 3DS, nothing could make me intersted

NPG, I will buy pretty much whatever the price

3DS: sold

NGP: under $300, MHP4

3DS:  Availability

NGP: If it does something significant that my phone (Droid 2) and 3DS can't.  I'll already have graphically impressive games, music, movies, internet, etc.

Nothing. I was born to buy Sony products.

3DS: Already pre-ordered.

NGP: 5 or more good games, atm it doesn't have that. Might change after E3 but I doubt it. It'll probably be the first Sony console I don't buy in the launch period.

3ds = they will have to sell it for $99 US or less...

NGP= Sell it for $150 US or less...

Until i play the NGP, i won't see the reason to spend the money on it.  Like others have said, most of the stuff it does i can do on my cell phone.  The games will decide whether there is reason to buy it.