Wouldn't you want to try to get an original model Vita? The screen of the original is better. Though beyond that I'm not knowledgeable enough to know whether or not the Slim had changes that were actually improvements, like on form factor or something.
Anyway, good luck with your third attempt.
I got an original one this year and I'm starting to regret it, since I had the option to get an Slim. The Rear Touchpad is waaaaay too big, it's not confortable for me to hold it for long play sessions because of this. The screen is amazing though.
Sadly everything about it is so expensive.
The games are already rare too, at least around here, damn.
You're from Brazil, right? I got mine with an 8GB memory card, I'm trying to buy an 32GB one because the 64 ones they sell here costs twice the price I paid on mine. It's absurd, specially considering Vita's digital games on PSN are way cheaper here than the physical ones.