According to Taylor, L5 will be released in the next 24 to 72 hours - so you might as well wait. A lot of the Laravel specific components (The Illuminate components) still work the mostly same. Therefore most of what you learned from 4.2 will carry forward to L5.

Laravel 4 is easier to understand in my own opinion so i believe a knowledge of L4 is not a waste as it serves as a foundation

Okay thanks for the input.

after asking myself (and here in the forum) the same question, i can give you the clear answer: L5 without any doubt.

Sure, L4 is a litlle easier at the beginning, there is more documentation and snippets and projects of it as for L5. But sooner or later you will (and have to) change to L5 and start all over again, since the structure is different, there is made extensive use of namespaces etc pp

I strongly can recommend the Laracast Series. (Little) Money well spent!!!

Here's the link to my thread: http://laravel.io/forum/01-25-2015-laravel-4-vs-5