I would say a Link to the past. I&II are good games but are much harder to figure due to no guidance out and therefore are less naturally/aromatically fun. They are good but they are not priorities imo. Also imo ALttP is the easiest game to 100% and still make it worth doing. It is NOT an easy/wimpy game though. Its full of content, puzzling and fun. It is the classic Zelda Story.
You probably should get A Link to the Past, since it's the favorite of many Zelda fans. It's not my favorite – it honestly didn't stand out to much in the series for me, probably because I played it after many of the other games – but it's a good one to have.
Legend of Zelda, however, is one of my favorite games in the whole series. Just saying.
I'd suggest getting LoZ and AoL because you get two games. I'm currently playing the original LoZ from the Wiishop and have enjoyed it, though it is a little strange since I've only played the more recent Zelda titles. However, lots of people are very fond of ALttP, and it is an excellent game as well. But for getting more games out of the 1200 wii points, get LoZ and AoL.