I find that accessing the Table of Contents when reading an ePub book to be unacceptably slow. I like to take a look to see how many pages the next chapter will be so I know if I have time to read it or not.
In an LRF file, I can do this easily, but when loading up an ePub TOC, it can take up to a minute or more just to load.
I also prefer the fact that LRF's have actual pages as compare to ePub that just have location numbers.
These are only personal preferences though. I think trying both formats and then deciding is the way to go.
dordale