I prefer both. I use amps with switchable channels and reverb, and one has tremolo as well. I have had programmable multi-FX in the past, but I don't have one currently, and I kind of miss the versatility and flexibility. When I used the multi-FX, I ran the amp clean and dry, to reproduce what was coming out of the FX. There have been times when my FX unit died on the gig, and I just got out my spare volume pedal, ran it in my amp's FX loop, and used the amp's channel switching and reverb. The last time that happened, it sounded so good that I never bothered to replace the FX unit, but I may get another one soon. If my amp goes down, I can run the FX unit into the PA and get through the gig. Multi-FX built into the amp may be more convenient to set up, but if it dies you've got nothing! Of course, back in the old days I used a bunch of pedals into the amp like everyone else.