Should I join the military as a 25B or stick with certification and finish my Bachelors in Computer Science?

Finish your degree. Joining the military is a big commitment, so do not join just for the money.

If you are all about the money, finish your university until you get MS in Computer Science in INFOSEC. In the long run it can get you up to +100K with less than 1 year experience in the field out at civilian sector.
When I was working as IT Specialist INFOSEC (Cyber Security Engineer) I was making 80K with only BS in Computer Science in Network Engineering and 11 years of experience in IT field, but I am currently a IT Specialist SA (Systems Administrator) I only making 69K, but I feel like I am contributing something to the advancement of humanity.
It is all about what you want in life I guess. My military career was bit rough at beginning and in the early middle, but I am enjoying being specialist in my field and in military for 1 weekend a month, 2 to 3 weeks a year. I do OK in the civilian life, there is a light at the end of the tunnel for me out side of military.
If you want and thinking about to join the Army. I will say from experience, 25B is a basic help desk work in the Army from E-1 to E-5. If you want to do more and gain experience in advanced IT work, go for 17C. 17C at least you get to dabble in policy and planning for IT infrastructure. Or 25N, here you have chance to play with network switches and routers and many other network of things.

You have many options available to you.

- If you join the Army for 25B you may be able to take advantage of programs that can help pay for those student loans you may be accumulating in pursuit of a degree. Remember that 25B is only one of the Military Occupation Specialties (MOS) within Career Management Field (CMF) 25. 25B focuses primarily on day-to-day computer workstation and internetworking duties. Some of the other CMF 25 MOS focus on telecommunications, infrastructure and/or enterprise networking. One of the other CMF 25 MOS might better suit your particular career goal.

- CMF 25 is not the only Army career field that involves information technology either. For example, a relatively new MOS is 17C which focuses on Computer Network Defense (CND) or Defensive Cyber Operations (DCO). Be advised that 17C is a highly challenging MOS with demanding skill and security requirements but also can be very rewarding. Success at this MOS would place you among a very small, select group of IT professionals.

- You don't have to resign yourself to the Army. All branches of service have IT/Cyber Security programs. One of the other services might have a program that better suits your long term career goals and interests. I know through association with some of its members that the Air Force has a very exciting and challenging IT program.

- If you feel that a full-time military membership may hamper your ability to pursue your career or education you might want to consider a reserve component enlistment. Members of the reserve components (e.g. Army Reserves; Army or Air National Guard) receive the same training as their active component counterparts. This would allow you to pursue outside goals while maintaining your military career.

- None of the above would keep you from attending OCS once you've established yourself in the military. Many officers and senior enlisted folks I’ve worked with throughout my career (including me) find that officers who started out as enlisted members have a better understanding of leading soldiers.

- And don't forget about the Army Warrant Officer Corps.

I've heard many times that civilian employers find the leadership, problem-solving skills and discipline, developed through service, to be highly desirable traits when selecting employees. Military membership would definitely help you to be more successful in life regardless of the path you choose.