My personal favorite is Makashi. I use it when in combat and it works great, I rarely lose. What's yours?
Vaapad. Just because this picture is so awesome. It and Soresu are the only forms I can really only remember by heart. xD
Niman, take the time to master it at the highest degrees and you master all areas of lightsaber combat entirely.
If you're talking video games, I wouldn't know because I don't play them. If you're talking generally, then I'm for Soresu. I'm probably (OK definitely) influenced by Obi-Wan here but it fits my preference for non-violent solutions where possible, while also making its masters almost invulnerable. I like the idea of using a precognitive meditative state too - let the Force do the work for you! In the end, it depends on your situation and who you are fighting against. Everything considered, Vaapad is probably the most effective technique - it's too bad that two of the three people who mastered it fell to the Dark Side!
Only one person has every mastered Vaapad, the other two practitioners fell to the Dark Side after using it therefore they were not masters of the form. It is, however, the most deadly form of lightsaber combat IMO.