A Very good question.
Here's the thing -- Gameshark 1.x to 2.x are actually programmed by Datel, and rebranded for interact. The newest gameshark is based on pelican's codebreaker, as far as I know.
Personally, I would recommend Action Replay MAX 3.0.
It's got some nice features, and access to the internet.
It also bypasses the copy protection in some reguard, using the UMCDR format.
Basically, you can run arbitrary ELF files from a self-burned CDR with it.
You CANNOT run copied games with it.
... But you can use sjeep's exploit installer and a handy PSX boot CD.
Just name the exploit installer autoexec.elf, and add the proper files.
Then you can use something like gsloader, cogswaploader or the like to use CDRS and DVDRs. It can be done. Should it be done is another question entirely. I use gsloader with my PS2 v2 with duke's trayswitch for booting mostly homebrew code and emulators. Mmmm, commodore 64.
Anyway, that's a wrap. If you want more information, google fer it yerself or check out ps2dev.org -- happy hunting.
If at first you don't suceed, Pull the trigger again.
See bash. See bash run. See bash run GCC. Run, GCC, Run!