It depends on the body of water, wind/wave action, fishing style and most importantly the bottom composition.
I have a few different setups:
For sandy bottoms with little to no wind or current, I have a 100' rope caddy with an 8lb. window weight tied on. For areas where there is current like an inlet or river, I prefer a drag chain approach. Basically, you need a 3-4' length of heavy chain, a bicycle inner tube, some heavy zip ties and your anchor rope. You feed the rope through the inner tube, secure it to the end link of the chain. Apply some WD40 or generic vegetable oil on the chain in case it is a little snug and pull it back through the inner tube. Once it is through, zip tie both ends. Now you have a drag chain anchor that can be used almost anywhere including open saltwater. You can even make different sizes for your different fishing styles.
For rocky bottoms like rivers or jetties with fast moving current, the last type of anchor you want is a grapnel style anchor because it can get hung up and be difficult to get unstuck placing you in a very precarious position and unsafe situation. More than a few have had to cut the rope and lose their anchor around bridge pilings around the bridge complexes here in VA.
For vertical presentations around heavy rock structure, I actually prefer a "wreck anchor" which is an anchor that has bendable tines on it that will catch on rebar, rocks, sunken boats, etc. and hold your position pretty well, but if you get in a situation where you need to pull anchor, you just pull firmly and slowly. The bendable tines will straighten out enought to break free of the structure, allowing you to save your anchor and re-bend the tines for your next spot.
A helpful rigging tip for the grapnel or claw style anchors is to use the zip tie/monofilament trick of tying your anchor line to the bottom of the anchor and securing the rope to the anchor eyelet. That way when you get stuck, you can pedal over and pull on the rope until the top part comes undone freeing the anchor rope to pull the anchor in the opposite direction and freeing it.
For ponds and shallow water, I either use a 1.5 lb anchor with 25-40' of rope or if its shallow enough, an 8lb. vinyl coated dumbbell (for my son's kayak) or a stake out pole.
The last anchor I have is a technique specific anchor for my area but the approach can be used in other situations. It is a "piling anchor". Basically, you take a lightweight wrech anchor like mentioned above and tie it to the end of your anchor line. About 8 feet above the anchor, you install a couple styrofoam floats simply for visibility of your anchor line and then the remainder of your line (about 25' in total length is all that is needed). The conept is to use the moving water as your anchor. You pedal up just ahead of an obstruction where current is flowing around it aka a bridge piling or dock. You toss the anchor perpendicular to you and allow the current to sweep the anchor behind you but on the other side of the piling. When the line starts to catch on the piling, you loosen your grip on the anchor line and slowly drift back with the current. If executed properly, you will have your anchor on one side of the piling with the floats visible, and the tension created by the current against the piling will actually hold the anchor line in place and allow you to tie it off on your anchor cleat. If you hook into a fish, drop the anchor line, fight fish, then pedal back up to your position and re-cleat your line.