I'd just like to point out a few things:
First: Wiimmfi is used a lot, especially on AC:CF. The old "oh noes it's too slow" excuse is no longer valid, as the disc program fixed that. There is also a patcher I created for Wiimmfi that can also change "Nintendo WFC" to "Wiimmfi" - I cannot share it here but you can google my username, and find my website.
AltWFC also has issues, so please do not recommend to use it. Oh, and town to town mail works IF YOU ARE IN THE TOWN OF THE RECEIPIENT WHEN DELIVERING THE LETTER (So that their Wii directly gets the letter). As WiiConnect24 shut down in 2013, and no progress on the WC24 Mail section has started, we are currently stumped for ways to send from x town to y without being connected.
A large userbase plays on Wiimmfi, and, if you know whom to ask, Wild World can also be played on the server (however the userbase is considerably smaller)
I wish I could explain in more detail, but the moderators here do not allow me to do so, and I do not wish to go against the moderators.