I'm going to vote for the zombies. Make a creepy environment MUCH more creepy...plus they give you so much tension to run, run away as fast as you can!
Ganados seem like more advanced zombies. The only zombie thing they do is grab Leon and put him in the air, biting him. But, they have weapons. So does their African counter parts, the Majini. Sad thing is...Chris and Leon AND Sheva ( Including every merc ) usually have powerful freakin handguns. And later on...get bigger and powerful weapons. Until, the Majini have guns....and a big Ganado comes up with a red Beret and a bullet proof vest..with a big Minigun that has loads of ammo on his backpack...basically, you have the guns, you have the power to kill them all. Which is all the guns. Except for those big District 9 alien looking things that have white bubbles on them, and that odd transformation of some of the Soldier Majini...and the chainsaw guys. Oh yes and those odd gray things that have to be shot with a missile, or by shooting them in the correct spots. And the even creepier one...Iron Maiden. ( Wtf. ) Those are the only tension giving Ganado and Majini.
In the first Re's, the pistol sucked, and shotgun shells were hard to find. Which made you get more tension. PLUS aiming was harder then the newer games. Thankfully, the old styled games out number the new style games. Outbreak File #1 and #2, RE 1-3, CV ( and CVX ), the praised REmake ( love that name!
), RE 0 and the first beta of RE 4. Only 3 new styled ones, RE 4 and 5 and a Iphone, Itouch and Ngauge phone game for Degeneration.