I know these stones are used to enhance your weapons and armor.. Can someone tell which one better and how to get the better one? Thanks

Try uesp.org, everything's on there.

Sorry .net

You get a sigil stone by closing an Oblivion Gate. The level you get is determined by your character level at the time. The exact one you get is random. If you save the game right before you grab the stone, you can reload and try again till you get the one you want.

Here is more on the levels and types: http://www.uesp.net/wiki/Oblivion:Sigil_Stone

I highly recommend that you try and get as many different Sigil Stones as possible. You find them very useful after they become Transcendent as they have the most powerful enchantments in the game!

Some of the Sigil Stones don't get any better with level, because their effect is an on/off one, like Water Walking or Night-eye. So if you get those at a low level, they work just as well as Transcendant ones. If you need to close a gate before level 17, try and pick one of those and you won't need to replace it with a better one later.