Wow, it's definitely a toss up between the R-Type R-9A Arrowhead and the Gradius Vic Viper! But if I was picking these purely on aesthetics I'd probably go with the R-9A Arrowhead. Gameplay-wise it would be the Vic Viper.

I always loved what R-Type was trying to do but it always seemed clunky and not quite as fun as Gradius. :)