Iron Man was much closer to the original story.  It was a watchable, enjoyable movie.  
The cool part of Transformers was 30 seconds of robots battling on a freeway.  The rest of the movie was for 13 year olds.
Personally I think the Mark II Iron Man suit was much cooler than the car commercial that was Transformers.
It remains to be seen whether Tony Stark can hold up to the Sisterhood of The Traveling Pantsparty.