Multi Theft Auto (MTA) is an open-source software project that adds full on-line gaming support to Rockstar North's Grand Theft Auto: San Andreas PC game, in which this functionality is not originally found. It is the first open-source modification that adds a highly customizable network play element to a commercial closed-source single-player PC game. Developed as an experimental piece of software for earlier Grand Theft Auto series, Multi Theft Auto has become an advanced multiplayer platform for gamers and developers. Our software provides on-line gaming for dozens of players running user-generated gameplay content and scripts through a Lua virtual machine, and is freely distributed under the GPLv3 license.
MTA:SA is one of the San Andreas Multi-Player mods. Half of the players are here, other half - on SAMP. Can't say it doesn't have problems, but I really like the working Towtruck. ;D The game is almost fully moddable, which is great. Sa-mp has a lot easier gamemode system. But still MTA is great.
Yes, It's a way better than SA-MP, because of the LUA language and the overall structure. Gamemodes may range from Roleplay to DM, so possibilities are nearly endless. The only problem is that a complex Roleplay script can run very laggy on the server, and the clientside scripts may lower your game's performance.