Bamboozle, the one I like the best is Fly-tite. It's fairly thin right out of the bottle, doesn't thicken or discolor and remains flexible. Chris Helms put me on to this one. I also use several others but always have to thin them with head cement thinner. I haven't used any water based cements but I would imagine water would thin them. that's just a guess.
Just got a chuckle. I read the bottle and it says not to thin with Vodka. Oh well.