I am certified in both Openview and BMC Patrol. I know folks that know CA and Tivoli. I can tell you one thing for sure from my experience; If you don't implement the processes (philosophy, process, procedures) with these tools, they will all fail miserably to deliver expected results. HP has a good document which applies to any of the above called "A fool with a tool is still a fool". Good reading.
I think for breadth of coverage, stability of company, and ease of implementation (relative), I would pick Openview. But I do have a bias (I work for them).