Gear up or down? Gear down if possible - I want as much distance as possible from me and the hard stuff (i.e. planet earth). It also has things like wheels and brakes on it to help control the crash phase and perhaps absorb some energy.
Rwy or grass? Hmmm, depends on many unknowns and variables. The consistent thing about runways is that they are generally straight, smooth and hard (unless it's a grass runway) and may have arrestor systems if applicable. Grass areas alongside rwys can be straight, smooth and soft, but can also hide objects, ditches, holes, very soft patches etc. etc. that could be a big gotcha. I'd always go for a rwy as first choice.
I stress that the above are my thoughts only and that I never (thankfully) had to face such a situation in 30 years of flying.