Silicone lubes are slick and won't need to be reapplied as often as water-based lube.  If you're planing on using lube in water, silicone would be your choice because it won't break down as quickly in water.

Please Note: If you're using a silicone toy, it's generally suggested that you not use a silicone lubricant with it. Depending on the quality of the the silicone lube and/or the silicone toy, they may produce a reaction that will cause the silicone toy to break down. No toy or lube company can/will guarantee that they can be used together, so just do a spot test to be sure there is no reaction with your toy. Sliquid brand lube does not warn against the combination.