Can someone explain me the difference between alsjeblieft and alstublieft?
Alsjeblieft is informal. It has "je" in it.
Alstublieft is formal. It has "u" in it.
Edit: You can think of it as "if you like" or "if it pleases you". It combines three words. Als = if, je = you, and believen = to please"
Is one of them more common than the other in contemporary use? Or, are they both actively used, but with a formality difference?
I am not a native speaker, or even A1 according to testing, but from what I can tell, it's all formality. Same with using "du" and "Sie" in German.
Or "tu" and "vous" in French