Bought an ipad 4 before christmas, previously having the 2 and the retina screen is a massive must have. I didnt think it would be that much better but it is.
I dont know what the ipad mini has as an advantage apart from being smaller and lighter.
My brother bought a couple for himself and his son and they are very nice but i think i prefer the ipad 4. Retina, faster processor and i prefer the larger screen as you see more content at higher definition.
My mum got a kindle fire HD for xmas and whilst that has a great screen it didnt feel as intuitive as the ipad. The smaller screen also felt too small when browsing and reading content from the web.
I just think the ipad is the perfect device to have around the house and the kids absolutely love it. Back when i bought the first ipad 2, you couldn't get games like peppa pig, hello kitty etc on the android devices so that was an immediate down point. It just seems that apple have a better array of applications (perhaps the playing field has evened out now)/
Remember with apple, if you decide on the mini, you can always take it back and swap it even if you used it providing it's within 14 days.