I've been watching reviews on regs since I started diving a few years back, and my observation is that most newish regs breath very well, and are based on the designs of the high end and expensive regs.
From talking to LDS owners, and Dive Op owners what they look for in rental equipment is simplicity and durability at a low cost.
How good they are is based on use, abuse, and the service the LDS provides for the regs as well as the area where the regs are used. In land locked areas, the regs are mainly used in the pool, and in fresh water, so renting a reg is a good and safe option. In area's where the regs are going to be used in the ocean, service becomes more of an issue as salt and sand take a toll.
I think renting equipment in most resort areas is not a poor option, but before doing so, I'd talk to the service manager, and ask about their maintenance policy.
For the most part regs are rather durable, but they do need service, so that becomes the key. Like a rental car a good shop needs to change the oil so to speak based on use. If they just say they do annual maintenance, that IMO may not be good enough as most manufactures recommend service more often if the reg is used daily for example.
For the $250 cost of a very good if not low end reg these days, I'd make this a priority purchase if one is diving more than a couple times a year.