They're completely different, but helpful utilities. I use DF all the time, Launchbar not as often.
I also feel that I can't live without DF, but that's just me. I bought a single license of DF back in 2008, and it's been upgraded since then - I don't know how they make money, but they're keen on keeping DF up to date. My GF uses Launchbar every day and loves it.