I'm trying to figure out a suitable encryption technique and after reading a bit, I figured the current AES 128-bit encryption is suitable for what I'm trying to do. However, this is more due to the wide-range use of AES than any other factor. So I need to know how the AES compares to the other finalists Twofish, Serpent of NIST's AES competition in terms of speed, security in software systems.
During the final round of the AES contest, NIST issued a summary of the 5 finalists on the topics of security, speed, implementation, and such. That sounds like what you're looking for, see sections 3 and 5 of the paper.
General ideas from the paper:
Rijndael had a potentially lower security margin than Twofish and Serpent.
Rijndael had better performance than Twofish and Serpent.
The Rijndael construction was arguably simpler than Twofish and Serpent.
However, this was published in 2000, 12 whole years ago, so it won't have the latest security updates on the algorithms. Rijndael certainly has more attacks against it due to the focus on it. But presumably a lot less has been put into Twofish and Serpent, so we don't know how strong those algorithms would look if they had the same attention that Rijndael had.