for the past week i have been testing modchips in some of my ps1 consoles and i have learned a bit with my own experiments. i was under the impression that the MM3 was the de facto standard when it comes to modchips, in some ways it is, but ill try to explain, i was testing out cheat carts and discs in my scph-1001 that has a MM3 installed, i noticed that when i booted into the gameshark pro 3.2 cart and picked out some cheats and then went to launch game, it would just freeze. the backup would boot without the gameshark cart just fine, so i tested a gameshark cd, and it was the same result, so i then tested just booting into gameshark pro 3.2 cart and quickly chose launch game without codes and the backup would boot, i also tested leaving the lid open when picking out cheats and then closing the lid right before loading the disk, this also didn't work. i then tested out this on a few of my other ps1 revisions, scph-5501, scph-101 PsOne "used the gameshark cd only of course" they all failed with using gameshark carts or discs.
so i started looking up some info on the MM3 hex and figured out that it used the internal oscillator instead of the ps1's, and something may be up with the lid switch monitoring because when opening and closing the lid the chip should see this and start the process over, i don't have any proof but i think this is the issue with the MM3.
" i also want to take the time to say that my backups and lasers are working fine, the discs will boot just fine in all of the ps1 consoles i have used for the tests. and the laser in my scph-1001 is upgraded to a BAM"
so i started reading up on PsNee and mayumi v4, i swapped out the mm3 in my scph-1001 with a Pro Micro running the latest PsNee code and it worked 100% of the time with gameshark cart and cd, i could spend as much time as i wanted in the cheat cart or cd, pick the cheats i wanted and then launch the game, no issues. the PsNee monitors the laser and when the laser moves to the sector where the wobble code is stored on an original disk the PsNee starts to spam the wobble code, when the laser moves away from that sector the PsNee stops sending the code, it monitors the SUBQ and SQCK insted of the oscillator, its really a smart chip
i then swapped out the MM3 in my scph-101 slim with a mayumi v4, tested out the gameshark cd and it worked, i was able to use the gameshark cd without issues, the mayumi v4 uses the ps1's oscillator instead of using the PIC's internal one, pretty good results with the mayumi v4.
all of the chips mentioned can be made at home with a simple pic programmer "or a USB cable for the PsNee".
So in summary, if you are just wanting to boot backups or imports on a north american console then any of these chips will work.
if you are wanting to use cheat carts or discs, then the mayumi v4 or the PsNee is the better option.
if you want a more future proof chip that may get some added features in the future then get the PsNee
if you want to know what my pick for best modchip for ps1 is then i would say PsNee