Depends on what you're using it for and what your preferences are.

Water-based lubes have the advantage of being compatible with any type of toy, and come in varying thicknesses so if you need more of a "cushioning" effect, you can get that by choosing a thicker lube. They're also the easiest kind to clean up, either on the body or when spilled. The downside is that they tend to not last as long as other types (this varies from lube to lube) and if you're more sensitive to certain ingredients you need to be careful about what brand you choose (glycerin and parabens are very common in water-based lubes, and these can have unfriendly effects on the body).

Silicone-based lubes are extremely slick, longer-lasting, and don't rinse off as easily as water-based lubes so they can be used in the shower. They can have bad effects on silicone toys, though (not always, but often), and tend to be thinner so they don't provide a cushion. They're also harder to clean up.

Finally there's oil-based lubes. These provide some glide without being as slippery as silicone-based lube, and similarly don't wash off in water without a little effort (which, again, makes clean-up a bit harder than with water-based lubes). But with the exception of a few high-end brands, most oil-based lubes shouldn't be used vaginally, and oil degrades latex so such lubricants can damage condoms very easily.