Be careful using FMX. Make sure you never link an IMVU account to it that you don't control 100%. If one of your accounts that is tied to FMX gets banned, they will stop doing business with you and you will not be able to get your money or credits that you have stored on the account. Also, any account you tie to your FMX has control over it. They can withdraw cash and credits from it. I found this out the hard way by tieing people to my account to sell them credits and getting my credits stolen and then having one of them get banned and now my account is useless and they will ignore your tickets.
Bottomline: FMX is good is you are very careful and never get into any trouble and can prove where all your credits come from to get limit increases.
IMVUCE is a good place, I use them often, aside from a background check for your first time, they are quick and easy to work with and I've never had ANY problems with them like I have with FMX and Anshe.