Like so many things in life "it depends" :')
I'm just a part-time player, so I decided that I didn't want (or need) to spend a lot on effects - so I have a Zoom G1X 'all-in-one' box. Cheap, but not too bad for a church setting once every couple of weeks.
If you were 'semi-pro' then I'd look at something like the Line 6 floor pods - there are some good deals floating around some of the stores in Australia at the moment if you look hard enough - but at over three times the price of the G1X,they were not for me.
If you're hoping to be full-Professional, then buy the individual items, and get "the best" you can. Probably start with a delay pedal, a distortion pedal, and a compression pedal. Those three should be a 'good start' - in that, they are the three effects I use the most in combination on my G1X (oh, and 'phase shifter' :')
As for what "the best" is - that too will depend on you, and what you are trying to achieve - you are looking for your "own" sound,