Tremolo systems. Nothing against it and a lot of my favorite players (Hammett, Hanneman/King, Dimebag, etc.) use it and I love listening to divebombs and all but I just don't want the added responsibility of having a guitar with a whammy bar. Besides, I personally find it more 'impressive' whenever I see a shredder ripping out a solo using a fixed bridge guitar.
Also, any guitar with all them fancy finishes, flamed maple tops and all those very 'colorful' aesthetics. A guitar with a plain black finish is much more beautiful to me.