Rios have a strong reputation for hard drives that die on you (and a 90 day warranty!). So even though their products look good on paper (and their new Carbon has one of my favorite features, on-board profiling) it's hard to recommend them. Creative's rep isn't much better.
They get no press, but I love RCA's players. They're MSC (Mass Storage Compliant), show up as a hard drive, with on-board profiling so no need for software. Just plug into any computer, drag and drop, profile on the machine and the new files show up in the database. And you can also have the option of folder navigation on the player. They're also very reliable, and come with excellent included accessories, like a sturdy padded carrying case that has cut outs for the screen and buttons, car kit, etc.
The iRivers have nice functions like line-in recording, built-in mic, LCD remote, and are also MSC. But they have some fatal flaws like no real shuffle mode and a flawed database creation tool that can't deal with long file names or WMA tracks.
I would say if you need a remote and line-in/recording capabilities, iRiver is a good bet. etc., otherwise I'd recommend an RCA Lyra.