Which of those Monster Hunter games is better for one's first Monster Hunter?
MH4 is a little better with tutorials, but MH3 has an overall lower difficulty. Therefore, 4 would be slightly easier to learn, but 3 would be easier to play once you do learn. With either game though, there will be many things the game doesn't explain that you'll just have to figure out through trial and error, and much of the game's mechanics defy general logic, or even regular game logic, so you have to go against what you think you know and play the game the way it wants you to. No matter which you choose, the series isn't very welcoming to newbies and you'll need lots of patience.
If you plan to play online, the 3DS version of MH3 does not natively have online play: you instead connect using the Wii U, and you need to have a wired connection for Wii U for it to work. Get MH3 for Wii U, or MH4 for 3DS if you want online. 3 actually has better online features, such as private messaging, chatting during a quest, better search features... all things that are strangely absent from 4.