So far, they both seem very reputable and are entirely female owned and operated. It's okay if they have different rates, I've never worked any job that's payed me more than minimum wage so it wont be a big deal. I'm mostly worried that if one of them finds out that I'm working for the other, that will be an issue for them for some reason.
Thanks for the reassurance too
The different rates may not be problematic for you, but as I think Jas mentioned, if punters find the same girl is listed for $200 on one agency site and $300 on another, they won't like it and will obviously not book you through the more expensive one so that agency won't like you either! It depends a bit on the punter community (forums etc) in your area - they can be very important in the US, I think, but in places where sex work is legal there seems to be less need for tight communities of clients+prossies. But it could (at worst) somewhat tarnish your shiny new reputation at an early stage because some people might automatically think of the most negative explanation (that you are somehow trying to trick people) rather than the right explanation which is that you just want to spread yourself around a bit.
So watch out!
I would do one agency at a time. For example, when you first join an agency you'll get a rush of bookings from all the newbie-hunters so you'll want to be maximally available to take advantage of that. Then when that dies down, you'll really find out for sure whether an agency has your best interests at heart (do they still market their "old girls" or do they just let them fall by the wayside as more and more new girls join?) and if they don't, then
that is the ideal time to leave them and join a new agency, or join a second agency in secret, or set up as an indie.
But do bear in mind that punters are not stupid so they will often know as much about escorts' careers as the escorts themselves; they can quite easily 'follow' you around the Internet if you're popping up on different sites with similar pictures - and if they see you have different rates in different places, again, they might think you less professional and possibly less reliable. Sometimes I think I'd like to have a separate indie identity for just massage appointments, but if anyone recognised me they could kick up a bit of a fuss if they decided I was somehow trying to deceive my clients into paying more/less or getting more/less services, so I really don't think it's worth it. It only takes one slightly obsessive stalker-type (he need not even be obsessed with you in particular; certain individuals out there are, it would seem, just obsessed with knowing as much about prossies as they possibly can) to turn a potentially fun opportunity into a total pain in the bum.
There are a lot of guys who like to only see new girls, too, so if they end up seeing the same girl twice because she's lying about being new, it could be a bit awkward!
On the other hand, I am definitely firmly in the "avoid punter forums" camp (if only because I'd rather get valuable feedback from my genuine clients and reading angry rants about sex workers, specific ones or in general, just makes me want to quit working entirely, which isn't good for my bank balance!) so I wouldn't advocate running your entire business based on what certain small groups of backbiters and gossips might say about you on the Internet. That's a direct route to insanity and/or bankruptcy.
So if you want to join both agencies at once, do so. But be aware of all of the possible consequences so that you can make a truly informed decision either way.