A "disklabel" defines the boundaries of sections of the hard drive. The MBR does this same thing. The GPT format does the same thing. They are different ways to do the same thing.
Here's an analogy: it is like having a text file that says:
Prefix=Mr. FirstName=George LastName=Washington
and another file that says:
[FamilyName:Washington] [FirstName:George] [Gender:Male]
Both descriptions provide essentially the same details about the person, but the technical ways that it is done are a bit different.
If you use a BSD operating system, it will likely rely mostly on the BSD disklabel. (In fact, some software will call the BSD disklabel a "bsdlabel".) If you use Microsoft Windows, you're more likely to rely more on the information in the MBR. (I'm not commenting much on what supports GPT, since it is newer and, as I write this, specific details about support have been changing over the years. Basically, though, the GPT is another way to record the same sort of information.)
The BSD disklabel can co-exist alongside with the MBR. Both the BSD disklabel and the MBR describe boundaries; these are separate descriptions, so they don't affect each other. (It only makes sense to have both of these descriptions provide identical values for the details. If the different descriptions are providing different values, that would be confusing because there would be some question about which record is more trustworthy)
Which one do you want to use? Well, if you're using a hard drive over 2TB, the answer is not MBR. (It may be GPT.) Beyond that, the answer is probably going to depend on what operating system you're using. If you use multiple operating systems, you might use both.
