hard pipe pros, solid, won't move, permanent. Great if you aren't swapping out sumps and rearranging stuff. Looks neat and clean. You could also paint it if you wanted to.
Cons-won't move, permanent without cutting etc. if you redo your sump down the line chances are you will have to redo some of your plumbing
Soft pros-flexible, put it where you want, no elbows etc to glue and mess with. Easy to replace
Cons-flexible, make sure it's really in where it needs to be and secure. Nothing worse than knocking flex tube loose and coming home to a flood. IMO can look kind of sloppy.
I debated the two myself and ended up going with PVC. I have that peace of mind that the plumbing is solid. I know it's not going to move around and leak if something falls over and bumps it. people don't often look at the business end of the tank but when they do it looks neat and tidy.