You can also take out your SD card and put it in your computer's harddrive - if you have an SD reader, that is. Your computer will then prompt you on what to do next to save the images.
L/R Buttons
Pros
Faster to take screenshots
You don't need wifi
You can save a bunch on the sd card
Cons
Having to power down the system to take out the sd card
Screenshots are lower quality
Miiverse Posting
Pros
A bit better quality screenshot
Easily accessed on the computer
Cons
It takes longer to make one screenshot (hit the home button, sign in, make post < simple, but a little time consuming)
You need wifi connection to post it
If you have a Miiverse account, press the home button to minimize the game then post it onto Miiverse. You can access Miiverse basically on any electronics.
You can use webrender.net/imgur to upload screenshots from the 3DS. You do not need to take out an SD card, which could be potentially dangerous if you use the digital version of the game.
what i do is take the screenshot with the L and R hinges and then press home button and upload and post to miiverse.
you can then access your miiverse account by signing onto the website online. i use miiverse as the picture quality is much better.
i would probably take more screenshots if i had a acnl tumblr though.
Miiverse is one of the easiest ways. All you need to do is minimize your gameplay and click it. It's quick and fast to access and it has a better quality then using "L+R".
For higher quality screenies you can pause and take a screen shot of both screens using MIIverse, that way you can get a good pic of your bottom screen w/o using your camera, and then you have to post it on there, and you can access it via going to the site on your browser and just save it to your computer from there. And I didn't have to pay for MIIverse?
Googled it, back 2012, minors under 18 had to pay 50 cents to use Miiverse. This was removed after the release of Miiverse on the 3DS. Or what not, it might be a parental control feature (but to be honest I don't really care). It was to prevent little kids from spamming and so on Miiverse. ?\_(ツ)_/?
The same thing goes with the New 3DS's browser. If your under 18 and you view anything ...uh..... "Adult". You have to pay 30 cents to get access in the browser.
i just take screenshots in game, use the 3ds browser and upload them to facebook. that's an easy route, might take a minute or two depending on your internet connection.