I used to use all rack mount stuff for effects but in my old age, I have gone to single pedals, its nice to be able to be modular and switch things in and out as needed. I have a couple of different distortion/overdrive pedals and just pick the one for that particular need. I think its probably more expensive but the versatility definetly works for me. Here are my must haves:

Overdrive / boost - helps dirty up my Vibrolux
Distortion - like to play heavy stuff sometimes
Chorus - great modulation effect to make your should thick and wet sounding
Wah Pedal - i have a mutron auto wah and a old crybaby
Delay - if im the only guitarist i can fatten up melodies, great for leads, picking patterns
tuner - i love my fender pedal tuner

Hope some of this helps.