Best $500 camera today

Hi I've been searching around for answers but I couldn't find anything really satisfying.

I currently have a Nikon D90 which takes amazing photos in clear light but not that good in low light. And it's quite chunky and heavy (I'm travelling quite a lot).

I'm looking for something more portable and lighter. I've found a few references on various geek websites (Engadget, The Verge, etc.) and those cameras came up :

NEX-5T or NEX-6

LUMIX GF6 or GM1

SONY a6000 or RX100 (mark I or II)

I don't really care about changing lens. I'm after the best picture quality (especially in low light) and also good video recording (Full HD). I want to take nice portrait and nice landscape shots (in particular sunsets).

My budget is about US $500-600.

People have been praising the RX100. Would it be the best choice?

Thank you guys for your feedback !!!!

G.