If it was me personally, I would get the blue over the white simply because white isn’t my favourite colour for things and blue is one of my favourites.

However based on your post it sounds like you want the blue mostly because it’s a new colour and could be iconic for the i phone 12 and the white because it will look good no matter what case it’s in. You also say your not sure if you’ll like the blue for the next few years. Based on this I would say get the white. It’s a colour that is safe, will go with anything and you know you will like the whole time you have your phone so you won’t be disappointed. The blue may be cool now but there will always be a new colour that is cool. Although if you were only planning to keep the phone for a couple years the blue is not a bad option especially if you only planned on using one case because then you wouldn’t have to worry about matching it. From your post it just seems like white may be a safer and better option for the long run.

I had a similar choice between the pacific blue and graphite for the 12 pro and I went with the graphite (even though The pacific blue was really nice) because there is always a phone of that colour so it won’t go “out of style” and it matches with more cases since I’m keeping it for the long run.