I have not one, but two Vitas now. Probably sold out of all but the 3G model as the superior OLED (PCH-1001) model is now out of production and will soon be replaced on store shelves by the inferior LCD screen models. You are not required to use 3G, it can be disabled in the system settings, but then you know this by now.
As for the 3DS, I have an original model and have had no issues with it... aside from a severe lack of Streetpasses.
Vita is by far my favorite of the two systems. Some titles available for the Vita I recommend are:
Asphalt Injection - Arcade style street racing.
Lego Batman 2: DC Super Heroes - Best looking Lego game yet made for a handheld.
Rayman Origins - A solid platformer.
Playstation All-Stars: Battle Royale - A very underrated Super Smash Brothers clone that is quite addictive to play. If you own a PS3, it's cheaper to buy the PS3 version which gives you a PSN code to get the DLC Vita version for free. But you have to system link the Vita to the PS3 in order to download it per the terms.
Other than those, lots of people hyped up Lumines: Electronic Symphony. Well, I bought it, but I'm just not much a fan of Tetris-like puzzle games. Also bought Ultimate Marvel vs. Capcom 3. Game looks great and plays like the previous entries in the fighter series. Which is to say that I'm entirely terrible at it.
As for the 3DS, I've not yet played any games for the system which are all that impressive. Project X Zone is my favorite so far, and I've not felt compelled to put all that much time into playing it. I find myself more interested in carrying the 3DS around in my pocket in the hopes of Streetpassing other people so as to collect puzzle pieces and play Find Mii more than anything.
Vita also has an excellent Web Browser, which supports YouTube, and most sites that offer HTML5 video playback functionality. The PSN App offers a YouTube app, but there isn't any point in downloading that since YouTube works in the browser already. What is worth getting, for free, in the app store is the NicoNico Video app, which lets you access video streams on nicovideo.jp (one of YouTubes biggest competitors). Vita's Mail program can be synched with Yahoo, andother e-mail services, which is also incredibly convenient.