Neighbors park in street making it highly difficult for me to get in and out of my driveway without hitting their car, esp. during ice and snow. Should I go to their house and talk with them nicely, or write a nice letter explaining my situation.

Are you new to the area or are they? Go to the town first, and ask what the laws are regarding overnight parking and how close to a driveway cutout cars can be. Get it in writing.
I would go introduce myself, say welcome and all that, and then say politely but firmly that you need them to park further from your driveway.

Are they parked legally? How and why is it hard to get out of driveway?
If they are new, why have you not already talked to them to become friends or welcome them to neighborhood. I am sorry, I guess old fashion, but I would visit a new neighbor within a week of them moving in, and welcome them.

But you talk to them, show them the issue, and ask if they can help with the problem.

Unless they are actually blocking your driveway, I fail to see a problem.

I also have to wonder how difficult this makes your parking and exiting so difficult. Unless your street is very narrow, it shouldn't be so difficult. But if they have room to not park so close to your driveway, then, by all means. Talk to them.

Oh I have lived in such places... old cities or old parts of cities. Narrow streets of duplexes and triple deckers with a driveway every 50'....