When's the best time to go Scotland?

[Ricochet J]

Me and my mates want to go Scotland. We've never been before so we want to go soon. We want to
Climb Hills
Jump of high hills into cold waters (James Blunt style without the singing )
Wanna just relaxe

Any activities you can recommend? Furthermore when's the best time to go?

Ideally we want to move all around Scotland and not just stay in the city centre

Thanks