all of this IMO :
stage 3 is the one you want if you want the quickest option.
difficulty: they are all about the same. gentoo is easy to install, read instructions, type command.
length depends on your machine and how fast you read/type. stage 3's generally don't take too long ( it uses precompiled packages for the base). also, your network connection comes into play a little when syncing portage (unless you use a snapshot, but sooner or later you will want to sync before using portage).