Just an opinion here.
Employers typically drive which credential is most desirable.
Also typically, employers will not accept any outside cert. (welder performance qualificatin test record) without testing again themselves.
So from a students perspective it's most important to have the "skills" to pass a variety of tests, and to "study" by reseach the differences between the tests and balence that with the needs of the employers they intend to approach.
Having a "cert" is a good thing to get your foot in the door to take more tests! Welders are professional test takers, so you need to understand this and get used to that part right up front :)
I believe WABO certs. (Allen correct me if I'm wrong) are managed at a centeral location so that employers have a way to check to make sure somebody who shows up with a WABO card actually has continuity and is who he/she says they are. Similar to the Canadian Welding Bureau. The AWS only does this if the test has been conducted at an ATF (accredited test facillity).
Edit:
There is never a disadvantage to passing a weld test :)
and
You will note in Clause 5 that WABO welder tests when side bends are used is a little more rigorous (at least in my opinion.)
https://wabo.memberclicks.net/assets/pdfs/Welder/std%2027-13%20sixth%20edition%20november%202013.pdf.