I’ve pasted the specs below, but in my opinion the biggest difference is that the OpenFPGA - in its Analogue Pocket form - is an end-user friendly target. MiSTer is more “enthusiast-friendly” with more options and upgrades (including an recommended add-on to the basic kit).
MiSTer “tech specs”:
Intel/Altera Cyclone V SE (5CSEBA6U23I7) FPGA SoC with 110,000LE (41,500ALM) and 5,570Kbit of Block RAM.
ARM Cortex A9 dual-core CPU at 800MHz.
HDMI video and audio allowing easy connectivity to any modern monitor/TV.
1GB of DDR3 RAM that is directly available to both ARM and FPGA.
High-speed ARM <-> FPGA interconnect due to both being in the same chip.
OpenFPGA specs:
Intel/Altera Cyclone V FPGA
49K logic elements and 3.4Mbit BRAM
Intel/Altera Cyclone 10
15K logic elements
2x independently addressable
16MB cellular RAM
(128Mbit x 16)
32MB low latency memory
1x synchronous DRAM 64MB
(32Mbit x 16)
MiSTer “tech specs”:
Intel/Altera Cyclone V SE (5CSEBA6U23I7) FPGA SoC with 110,000LE (41,500ALM) and 5,570Kbit of Block RAM.
ARM Cortex A9 dual-core CPU at 800MHz.
HDMI video and audio allowing easy connectivity to any modern monitor/TV.
1GB of DDR3 RAM that is directly available to both ARM and FPGA.
High-speed ARM <-> FPGA interconnect due to both being in the same chip.
OpenFPGA specs:
Intel/Altera Cyclone V FPGA 49K logic elements and 3.4Mbit BRAM
Intel/Altera Cyclone 10 15K logic elements
2x independently addressable 16MB cellular RAM (128Mbit x 16)
32MB low latency memory 1x synchronous DRAM 64MB (32Mbit x 16)
1x asynchronous SRAM 256KB (128Kbit x 16)