You'll get the most current Health Insurance Authority comparison's [broken link removed] The Health Insurance Authority is an independant body to monitor the health insurance market.
From looking at Hibernian's brochure (here), you are covered for day-case and heart surgeries in the Mater Private and Blackrock Clinic (aka hi-tech hospitals). You don't have cover for GP visits, but in fairness, the out-patient excess on Plan B Options is only met by a small percentage of their customers, so VHI can't really claim the high ground on that point.
One thing that VHI might have over Hibernian is the number of consultants that are fully covered. I say might because I don't know how many either of them cover these days. Ask both insurers how many consultants are fully covered. At this stage, chances are they both cover similar amounts, but better to be sure first.
Also, do a search on here. I know a few people have spoken about their experiences with Hibernian/VIVAS so you might learn more that way as well.
Another option may also be to talk to the guys behind [broken link removed]. I've never used them myself and I'm not connected with them in any way. They seem to act as a broker, but they also seem to be the only ones dealing with all three insurers. However, they may charge you for the service.