I've seen ladies from both worlds and have had great experiences. Regardless of the business model, you still have to do your homework. I can sum things up like this:
1. I travel to Europe frequently and, as a result, do not have much of a track record here in the U.S.. I'm hard, if not impossible, to verify while at home. I find that agencies here in the US tend to be more "newbie-friendly" or are more tolerant of those like me whose profile is more in line with newbies. Agencies in Canada are highly reliable and are generally the way to go for me when I'm up north.
2. It's often easier to arrange an appointment with an agency than with an indie. Frequently, I simply don't have the time to do all of the upfront planning required to book an indie.
3. When I have been home long enough to establish relationships, I prefer indies in my local area. I generally can be flexible because I'm not going anywhere soon.
4. I share the concern about visibility and the high-value target that an agency presents, especially in an election year. I always request an outcall from an agency. The likelihood of a sting is less than an incall. I always use a hobby phone when booking through an agency.
5. On the subject of the quality of employer-employee relations, I've found it to be a fairly easy judgment call to determine which agencies treat their ladies well and which ones don't. Probably 15 years ago, I was traveling to Colorado Springs frequently and found a very good agency. I got to know the owner reasonably well. He once told me that the keys to success were to be low-key and pay your taxes