What level of electrical service should I order, for new construction?
Most houses have either 100 or 200 amp service. 200A service costs about 30% more, and I'd assume that cost is higher if you want to upgrade later. 

What you need really depends on a few things, but the simple ones are: if you have electric heat or hot water, then go 200A. The other big loads are things like electric dryers, ovens, air conditioning, and hot tubs. Most of those are constant, but air conditioning power depends on the size of the house, and of course in general a bigger house will use more power (more lights and other electrical devices). 

Here's a site to help determine the electrical service you need.

I would definitely install 200A service in a house >2000sqft, or if there was electric heat/hot water. If money was tight and none of those conditions are true, I might try to get by with 100A. 

Right now I have gas hot water/heat, in a ~1500sqft house with A/C, and don't have any problems. I upgraded my panel from fuses to breakers, but still stuck with 100A because I just don't need more.