Panel de Pon is the original game released in Japan. Tetris Attack is the modified game released in Europe/USA with the graphics changed to Yoshi. The Japanese version has more "cutesy" anime-style artwork and Tetris Attack features... well... Yoshi. I'm not sure if there's a difference in the gameplay so I guess it's just a matter of personal preference.
Unofficial English translation is available for Panel de Pon (the Japanese release):
[[link:http://www.romhacking.net/trans/1144/ www.romhacking.net]]
[[link:http://yaworg.googlepages.com/translationproject yaworg.googlepages.com/translationproject]]
