Warcraft 3 is easily my favorite RTS game. I suck horribly at Starcraft (but I still love it!) but WC3 I'm actually pretty good at. It's easier for me to manage (and micro-manage) smaller armies than it is to pump out 50+ units and fight with 4 or 5 groups like in Starcraft.
Ironically, one of my favorite WC3 units is the Necromancer.
Also, Tower Defence is great fun. :)