Cobras are very nice pliers, but just like anything else they do have their strengths and weaknesses. If you are trying to get a single plier to do as much as possible you might want to look into a pair of Channellock V-Jaw pliers (or if they can handle the plumbing size you work with, the largest size of "nutbuster" pliers) instead. They are a nice compromise between the Cobras and a pipe wrench.
A good pipe wrench is pretty much the beefy gorilla of the tool world. They are very strong, they grip very tightly, and they can usually do the job when nothing else will work. I would never get rid of mine, but I do use them less often now that I have other similar pliers. Pipe wrenches do have pretty wide jaws, so there are situations where they will not fit or work well.
Cobras have really thin jaws, so their contact patch is much smaller. This can be good or bad depending on the situation. Cobras also have quite a noticeable flex to the handles when cranked on hard which many find a little unnerving, myself included.
Channellock V-jaw pliers have more of a mid-sized jaw width so they are a bit more versatile overall. They grab tight (like the cobras and/or a pipe wrench) without having to clamp hard on the handles with your hands, and they are more beefy than a pair of Cobra pliers so they feel much more secure and stable under high torque loads.
I have and use all the pliers I just mentioned, and I greatly prefer a regular Ridgid pipe wrench to anything else when doing threaded black iron or galvanized pipe work. For brass fittings I prefer a Knipex Pliers Wrench or a Ridgid hex wrench to prevent the fitting from becoming marred. For plastic or metal house sink drain fittings I usually grab a Ridgid e-110 hex wrench. For something like a hydraulic fitting I use either a flare nut wrench, a Ridgid hex wrench, Knipex raptor pliers, a Vise Grip locking wrench (4lw, 7lw, or 10lw), or a Knipex pliers wrench.
Overall, I really find myself using my Cobra pliers a lot less than I expected to, because there always seems to be a better option if you have a wide selection of tools to draw from like I do. I could easily get along without my Cobras, but I would never sell my pipe wrenches. Even with a wide selection of tools, standard 10", 14", 18" pipe wrenches are still a necessity for some jobs.