Well I can't speak for Scotland (never played a game as any Scottish dynasty, oddly enough), but the British Isles are generally the easiest place to start due to their isolation. Ireland is a cakewalk and you can play at your own pace. Once you get past the 1066 invasion shenanigans, all you really have to worry about is conquering the other small realms and if you are Norway or William, maintaining your continental holdings. Saxon England is an especially stable and safe realm to play since I have never seen the continental factions don't have any de jure claims on your land, so you can slowly expand, build up your army, and Holy War the Muslims in North Africa and Spain to build up your realm. No HRE to potentially screw you over either. It is easy to become really powerful and best of all, you can play at your own pace.