Not necessarily saying which is the best, but here's info anyway:
4-in-1 Action Replay lets you boot imports, gives you added memory for games that need it, provides space to copy saves from the internal memory (games won't save directly), and provides cheats if you're into that sort of thing. Play Asia and other places still sell new ones.
ST Key lets you boot imports.
Racket sells a 1/4 meg memory cart that provides the extra memory for games that need it.
I've found that most games will save to my Action Replay, the only excepion was Resident Evil which insisted on saving to the internal memory but when I moved the save file to the cart the next time I loaded the game it found the save file and carried on saving to the cart.
This is one of the new versions without the port on the top. Not sure if this makes a difference or not.
I would def recommend the AR 4in1, the only drawback is that everytime the saturn boots a game it asks you if you want to enter a cheat code.
I have an Action Replay 4-in-1 on the way from Play Asia right now actually. I'm a little nervous though, because since buying it I've heard from a few people that it just wrecks the cartridge port. I don't really plan on removing it once I put it in though, so I should be okay i guess.
Yeah, I don't know why you'd want to remove the action replay once it's in. Hell, if I ever had trouble with my cartridge port, I'd just hard wire the thing in there.
We are prepared to live in the plain and die in the plain!
I will also like to recommend the Action Replay 4 in 1... No more will I have to restart my games due to the backup battery dying... For most the games I play I use it as a backup memory, not a direct "save to" device because for some reason most games I play just wont see it. Not a big deal though.
I haven't used the cheat part of it yet but I have used it to play imports, and it played every time. I would also like to add that the menu system is logical and clean, so the simplicity is definitely a plus.
Also about the cart port wrecking... so far I've had mine for the better half of the year and have removed it several times for transport, and nothing has gone wrong. I have heard that the cart port on the Saturn is inherently delicate so I would exercise caution and patience when removing/ inserting the cart anyways.
Got: Atari 2600, Atari 7800Pro, Commodore 64, Odyssey 2, Sega Master System, NES, Genesis Models 1-3, Nomad, Game Gear, Sega CD Model 1, Sega 32x, SuperNES, GameBoys, GameBoy Pocket, GBC, Sega Saturn Model 2, GBA, Nintendo 64, Playstation, Sega Dreamcast, Playstation 2 Slim, Nintendo DS Lite, Xbox 360, Gamecube, PS3 Slim
I also have a 4-in-1 Action Replay cart, it works really great as a way to play imports,cheat codes and backup memory when your Saturn internal battery dies. Sometimes I have to take it out and put it back for the Saturn to detect it, but its not a big deal.
Systems: Sega Dreamcast(x2), Sega Genesis(x2), Sega Saturn, Sega CD, Genmobile (portable Genesis), FC Twin, PSX, PS2(x2), GBA, SP, Xbox 360, N64, Showcase Arcade