Red Hat's product line is now split into into two tracks: Red Hat Linux (RHL) and Red Hat Enterprise Linux (RHEL). RHL is comprised of two offerings, Red Hat Linux and Red Hat Linux Professional, whereas RHEL consists of three variants-- AS, ES and WS.
First of all there is no RHL version 8.x. RH made a single version 8.0 and then jumped to 9.0. Generally, minor revisions (i.e. 7.1,7.2,7.3) contain bug fixes and are more stable than major releases (7.0,8.0). I am using RHL 8.0 and I am very happy with it. It looks stable enough for me and better (mainly in looks and feel) than the previous version (7.3). I have not tested 9.0 yet so I can say nothing about it. Another problem is that EDA software relies on libraries supplied with the OS. At the momment, most EDA software has been tested up to version 7.2 or 7.3. This is why many people prefer 7.3 to use with EDA. This does not mean that 8.0 has bugs, it is just not fully supported yet!
I've been using RH 9.0 on my Dell laptop for about 2 weeks now. In general it seems to be more stable and significantly faster than 8.0, particularly with USB 2.0 devices. In my opinion 8.0 was one of the worst releases of RH. The 8.1 betas, particularly beta 3 (Phoebe) is nearly indistinguishable from 9.0. If you want to be on the bleeding edge, 9.0 is great, otherwise I'd stick with 7.3