Kikou Ryouhei Mellowlink

Both has main character defeating mecha in flesh i.e. without being in one as they come up with clever ways to defeat mecha-of-the-week. 

Golgo 13 is realistic in its setting and Mellowlink that of a sci-fi future. Golgo 13 is a mysterious, high paid assassin and Mellowlink simply a soldier out for revenge. None the less, the characters share an intense determination, superior physical reflexes, weapon skills, and tactics. Gritty is a word used by other reviewers for both and I agree. Mellowlink dates from the late '80's and although Golgo 13 series from 2008, both offer crisp animation without a a bunch of CG glitz. If you liked one, do consider the other.