Apollo Vampire V4 standalone is a "modern" FPGA implementation of a 68k Amiga that is nearly 100% Amiga compatible but much, much faster and with updated graphics etc. http://www.apollo-core.com/v4.html
So: MiSTer if you're looking for an authentic Commodore Amiga experience and want to play old games etc, Vampire if you have a lot of money to spare and want to do "modern" things on a classic Amiga (fancier games, MP3 and video playback...)
You should also consider that Amiga emulation is very accurate and fast these days and you could just get a Raspberry Pi running UAE which would be mostly indistinguishable from the FPGA reimplementations once you're up and running.