Well, I trade with 3 market makers - OANDA, Saxo and UBS.
I've 2 accounts at OANDA. They are popular with most small time traders that come to these forums. They have one of the tightest spreads in the popular currency pairs. The fact that they use a Java platform means I can trade from anywhere, like hotels, airport terminals, etc. I generally recommend OANDA to those that ask me. I don't like the charts. They have limited time periods. For me I use only the 30-minute charts. They also use 11:00 P.M. EST and midnight EDT for end of day on their daily charts. That make the daily charts useless since that is in the middle of the Asian session.
Most traders don't like Saxo because their minimum account is 10,000 USD and the spread is around 5 pips, not 3 or 4 pips from the others. They do have an excellent platform. In fact, that is the only platform I have running most of the time. They also offer more currency pairs than most other online market makers. If you are a position trader, the wider spreads shouldn't make much of a difference. They weren't targeting the small time traders, but they are starting to. You can now trade as low as 50,000-unit lots in the majors. For other pairs, there is a 10 USD ticket fee.
As you probably know, UBS is the world's largest interbank FX market maker. They have much higher minimum account size. I was told that it is 250,000 USD. The best thing about them is that you can trade mulitple accounts in a single block trade. They are great if you trade OPM. I prefer their order procedure. You have to request a quote each time. You are given time to accept or reject the quote like it used to be when I was trading over the phone a few years back. Most others have what-you-see-is-what-you-get quotes. In the forums, I read about re-quotes sometimes. The banks don't. When they give you a quote, it is good for a few seconds.
