My simplified opinion would be this. A GS300 is like a smooth piece of chocolate;Refined, Elegant and all around great mid-size car. Thats where it stops for me though. The 3 Series Bimmer is more like a chilipepper in this respect. Its spicy, taut, and an absolute blast to drive. While smaller, and a tad less refined when it comes to ride smoothness, the 3 would still be my pick easy. Its just a much more overall good package. The GS3 is more of the ultimate medium family sedan, the 3 series is your little rocket, and if others wanna join they can, but their comfort wont be the best. I havent driven a 400 or 430 however and I hear those are quite a speed demon too. Anyway I digress... 3 Series wins by a small margin, but these cars target somewhat different categories of buyer. The IS300 (and up until it came out the ES300) are more direct competition.
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<img src='http://members.cox.net/inelson5/wooani.gif' border='0' alt='user posted image' /> The whistles go WOOOO!!! *BUBB RUBB FAN CLUB*