@amiga4ever
I have lots of experience with one of these two OS's but have never even seen the other in action at all. So any opinions I give would naturally be slanted towards the one I own and use daily.
In my opinion, if you a have a chance to try both systems without having to purchase either system first, then you should try out both and decide for yourself which you like better.
The official AmigaOS 4.1 GUI is Reaction, but MUI is also included for compatibility with programs which require MUI, such as IBrowse, YAM, SimpleMail, WookieChat.
Other than that, either system should meet the needs of the average Amiga user. System friendly 68K applications should work on both.
---
redfox