I personally asked my boyfriend to get me a purple one for Christmas because that's my favorite color although I contemplated the white, yellow, and green models momentarily. White's a very neutral, non-descript color; it has a certain elegance about it although it may get dirty easier (We'll have to hear from someone who actually has the white model because I don't know first-hand). The pastel yellow is very darling, and I'd say that both it and the white model will go well with any pierce you use with it if you plan on doing that.
From what I gather (correct me if I'm wrong), the Aikatsu! model is a little bit like a pearlescent white which actually looks very nice; if you were going to go with white anyway then you might just get this one instead. It also has the related deco pierce, does it not? On Amazon, it doesn't seem too expensive for the cost of the tamagotchi itself and the deco pierce ($65-ish). For comparison, the purple one I selected was roughly $50, and that includes shipping, and the Sanrio Character deco pierce I picked out was $20 on ebay with free shipping. That's about $5 more expensive than what you'd be getting out of the Aikatsu! Tamagotchi P's from amazon.com, and the sellers on there look like they have reliable feedback if that's the route you want to go.
I'm currently deciding between the white, yellow and aikatsu set one so I'm looking for pics of them(especially the aikatsu one)...
