I can't say I've played it on the GB but I have played it on the DS, my PC and the Wii. I enjoy the Wii game the most. You can have lots of animals, get married and have a kid. There's always something to look forward to in the game and the things you have to do to get someone to fall in love with you are fun.
I'm a huge fan of the Harvest Moon series, I played the GBA version "Friends of Mineral Town" for 2 real years (Not game years ^^) before I got tired of it X3 I don't own that one anymore, but I have the newest spin-off of the Harvest Moon series right now: "Rune Factory Frontier" for the Wii. I feel it's my favorite Harvest Moon game without a doubt, even if it is a spin-off. The Rune Factory series adds an extra air of fantasy to the Harvest Moon formula, keeping most of the farming and social elements untouched while adding dungeon crawling to the mix. In the version I'm playing, you can be an alchemist, blacksmith, and craftsman along with your farming and dungeon crawling. It's such a huge game!