Forehand: i would suggest anything between semiwestern to continental (mine is usually midway, i get plenty topspin when i want to). the nearer to continental it is, the more versatile, flexible and easily adjustable it'll be from shot to shot. it should be your default grip in the ready position
Backhand (1H): eastern, and you can still use it for the slice. some prefer semi-W
Backhand slice: continental
Serve: Going from semi-western to cont. to eastern: very flat >> some topspin/slice >> extreme slice (but less topspin In my experience, or rather, a lower bounce).
Volleys: continental; but for net-level backhand volleys you might go a little eastern (or the ball could pop up), usually when you're too close to the net.
Dropshots: continental or very close to it.
continental is the most natural, most intuitive and easiest to convert to when you have little time. you can still manage to hit high balls, and it's the most effective grip on low balls.
lastly, don't go too extreme until you have perfect strokes, so most likely, never
. I see plenty of wannabe nadal types, especially young kids as well as some teachers (during their matches) hitting with extreme topsin (or rather trying to) with their nifty Babolat's. Their strokes looked contrived, forced and they have more mis**ts than hits.