I have quite a few OPI's in my nail collection and they are always the first I grab. They are super easy to apply streakfree, the colours are amazing and unique! (not to mention they have way too many to choose from!) They are fast drying and super glossy!!!
They are quite durable and will last a 3-5 days without chipping! Some of the lighter shades you can use as a sheer with one coat or even build them up with two and feel as if you have two different colours!
They also seem to last for ages if properly looked after, but longer than any of my other polishes which often go gloopy and thick after a while.
It is also easy to remove, if you have a glitter or 'shatter' nail polish just hold the remover on it for a while then swipe and it should come off easily unlike some nail polish where you feel as if you are attacking your nail to remove the glitter pieces.
Easy to apply with 2 coats and dries reasonably fast. Comes in loads of different colours. They need to be stored in a cool place so that they don't dry. Their one fault I must say is when they get to roughly half full - a third full they do seem to start dying out and need to be chucked out.
Tips: Put them in the fridge they seem to last longer