Filler Question

What brand/kind of filler do you guys use to do your "final" smoothing of a panel? I have my doors and shell close enough to flat for me to be thinking about how I will proceed to finishing it off. I have been using Evercoat lightweight filler so far and it seems to really harden quickly. Maybe unreasonably, but I am looking for something that takes longer to kick so I have a little more time to smooth on a skim coat. I am mixing it with only the same brand hardener, should I be doing something differently? I have played around a little with the ratio, but it doesn't seem to affect the hardening time too much. Thanks for your help in advance! L8r

Jim