I'm using flexi on my Latex because it came with it (Home machine) At work, I use onyx.
At first I presumed flexi wasn't as good because I use onyx 8 hours a day at work, and I'm still learning flexi. A few months later, and I still hate flexi. Onyx is more polished, better laid out, it just seems better in every way.
The ONE thing I like about flexi is you can drag and drop a file into the queue... onyx for some reason doesn't let you do that.
But if I was using my home machine to make money, rather than as a toy / hobby, I'd pay for onyx in a heart beat. Onyx also has a trial. Flexi doesn't have a trial.. but you can buy a month worth of flexi for $60. You're looking at a couple grand for a fully functional rip.. If you have no experience with any of them, Give each a try.. They all work good, it's just user preference, and a few little things each are better at than the other. None of them are a bad choice.