Hydro's veg growth rate is nuts. In 10 days from clone I had big thick bushy plants. There is a reason most only veg for up to two weeks in hydro. It's because it grows fast.
If you let it, Hydro will wear you out. Running around adding all these useless nutes, adjust ph and so on. But some soil set ups are very hard to water.
Higher plant counts should definately be hydro. Both produce great nugs. The flower time is strain dependant though. So you won't save time per se during flower. But because hydro veg's so much faster you can yield much more herb than soil in the same period of time.
Hydro growth during veg can be up to 300% faster. To get a 2ft plant from soil it can take up to a month or more. In hydro you can achieve this in less than two weeks.