I use ID for surrogate keys using the Identity Property. If the column is not using the identity property I would be more likely to use Id. Since I haven't used SEQUENCE yet I haven't decided on what I would like there. I would learn toward ID if it is a being used as a Surrogate Key.

Having said that, I don't mind Id.

In my first job we used lower case with underscores and surrogate keys were order_skey.

I've moved from advocating lower_case_with_underscores mainly because most discussions I have on the topic the others don't like it or use it so I consider mixed case to be more of an industry standard. The only thing I don't like is Mixed_Case_With_Underscores. That just hurts my eyes, and I have a database a my job that is like that.