How much better is the MiSTer compared against the original MiST? It's a broad question, but it seems like this is an off-the-shelf replacement?
Some things are similar because MiSTer is a successor/descendant of the MiST project. But which one is better is a bit subjective.
Technically the MiSTer has a much bigger and better FPGA, a 110K LE Cyclone V with extra 800 Mhz ARM MCU on chip, versus the 25K LE Cyclone III of the MiST with a tiny MCU on the PCB.
MiSTer has HDMI out, an Ethernet port, and supports many more USB devices. ARM MCU runs a barebones Linux for all housekeeping such as loading files from SD card or act as FTP server.
The MiST on the other hand has two DB9 joystick ports than can receive Amiga style 2 button controllers, and MIDI ports which can also be disabled to act as serial port for connection to a real modem, allowing the ST and Amiga cores to use the internet for instance.
In theory MiSTer could run all of the MiST cores and has already cores that the MiST cannot handle because it has no space (486 and Genesis). That said not all cores were ported yet and there is no timeline when that will happen. Being fully open source means that developers work on it when they are willing. Not unlike SE in the very early days.
Another key difference is a MiST can be more easily assembled as the Cyclone III can be hand soldered, whereas the Cyclone V needs industrial equipment. This led to various clones popping up, and eventually Lotharek to decide stop production of the official MiST for now. In any case that means the PCB for MiST can eventually be produced by anybody. With the code being open source, that means anybody can pick up the torch if the original devs leave.
MiSTer on the other hand is built around an industrial FPGA education board which have become fairly cheap (not the case when MIST was created). This means there is a risk the company stops producing it, but two things makes this irrelevant (IMHO). First, current production volumes are fairly big as the market is broader for these cards (its not just for retro computing but used for university FPGA education), and second there are similar boards where the MiSTer code can be ported to. One person is looking at making it run on a VGA only board which is slightly cheaper, for example.
Looking at clone cards there are models of MiST with SVideo and Composite video out, such as the MISTICA, which can be appealing for those wanting to game on CRTs
So if you like the idea of 100% open hardware or want an ST core right now, or maybe want SVideo/composite, the MiST or a clone might be more appealing, Otherwise the MiSTer would be the state of the art (HDMI) with more expansion potential. Its also cheaper if you go for just the SDRAM expansion.
Also just to be clear the cores are practically the same between the two, there is no difference in compatibility (basically they are largely the same Verilog/VHDL code). Only exception is some cores run better on MiSTer (e.g. PC Engine) as the bigger FPGA allows them to be more stable. Game support is the same though.
Edited by Newsdee, Sun Feb 25, 2018 6:01 PM.