Animated & War for/Fall of Cybertron for me. But I kind of like Prime Soundwave because he reminds me of Slenderman.
Animated. So much personality for one so devoid of personality. Animated's pretty much gonna be my pick for every one of these threads. It just nailed the characters so perfectly, every one of them homages the previous iteratiosn while being new and creative, and evokes the personality of the character. The G1 design is also pretty cool.
G1. There's just something so iconic about it, and while a cassette tape alt mode is dated as heck, it just looks so unmistakenly Soundwave. Honorable mentions to the creepy "Slenderman" Prime Soundwave and the evil disc jockey Animated Soundwave.
All of them except Prime and Cybertron. Never seen what he looks like in Cybertron and the Prime picture posted below the OP is horrifying.
Device Label, which is technically G1-based, but with the added benefit of being a functional MP3 player. Sonicron. It has its tolerance issues, but I love the updated take on the G1 concept, using a device which is actually still (somewhat) in use.
TR Soundwave G1 Soundave WFC/FOC Soundwave Classic design is classic. Kinda hard to improve on perfection.
Soundwave will always be synonymous with his G1 design for me...it's one of those simple yet effective definitive designs along with Optimus and the Seekers IMO.