Personally, I loved the j2e translation of FFIV. I beat the leaving hell out of it when I was 13 or 14. This was about 10 or 11 years ago.
Now, since I can read Japanese and hack things on my own, I look at j2e's work as inferior. Especially compared to the scripts of later translations (in particular, the DS translation).
Plus, their translation left random bugs intact. Like take a look at the status menu, for example. In the normal game (Japanese, FF2US, or otherwise), there should be a level counter there. Because j2e hacked their main menu to provide for longer class names, the character name was pushed down a line, and the level counter was pushed into a place where you cannot see it. This is something I was able to easily fix long ago.
I personally hope that at the very least I can put out something comparable to the GBA translation of FFIV. I know I'm probably not going to top the DS version in terms of writing (though it's not going to stop me from trying. I'm personally not going to make everything as period-piece sounding as their script did, but I certainly want my script to have flavor!). But I'm going to do my best to make sure fans of the game are going to enjoy my version of FFIV thoroughly.
As far as FFVI goes? I haven't played much of the fan translation. I like it for what it does as far as hacking work is concerned. SkyRender did a Let's Play of his FFVI translation where he's constantly berating his script decisions, and I can agree that the script isn't that great. I haven't played the GBA port yet (I was waiting for the sound and color restorations before I bothered, and now I simply don't have the time). I do agree with many of the changes Woosley made, though, simply because they're good localization. "Terra" instead of "Tina" because it makes the name sound more exotic, etc.