This was seriously too easy to answer. However, it is a tie for the top and as such I shall feature my favs. Yet here is a quick factoid about Arrancar. The word itself means “Ripped Mask” in Japanese, hence a hollow who has removed its mask.
Ulquiorra Cifer
I am pretty sure you saw this one from a mile away. As mentioned previously, loved him from first viewing. Whether he was a bad guy or not.
Grimmjow Jaegerjaquez
How can you not love Grimmjow?
Nelliel Tu Odelschwanck
Absolutely adorable, sometimes annoyingly so, but I warmed up to her and she quickly became one of my favourites.
Coyote Starrk
I really liked his laid back attitude plus his power was pretty awesome.
Who was your favourite Arrancar?
All About Anime and Manga 
Your thoughts?