Good idea or bad idea once outside the major cities. I'd like to visit small Polish towns and see countryside. How are the roads, driver safety, etc.?
You can get almost everywhere by public transport. But of course if you want to see small towns and countryside you will see more having a car. Polish drivers are generally more aggressive than we are used to here. Defensive driving should be your answer. When driving you always take chances anywhere. But I drove there and am still here.
I agree with Ilja - public transportation will take you just about anywhere you'd like to go. If you're uncomfortable driving yourself for day trips out into the countryside you could probably hire a car with driver for the day for about the same amount you'd spend for just the rental. We did it that way a few years ago to visit the ancestral village of my wife's family outside of Krakow. Worked out great and we even had a Polish translator with us at no extra charge.
We've been to Poland several times, and I agree - drivers there tend to be more aggressive. Just like any country, there are certain "unwritten rules of the road" that drivers in Poland seem to follow that we aren't familiar with.
Keep in mind that road signs are all in Polish. We've been in the countryside before, and it didn't seem like there was much in the way of good signage, etc.
I agree with the suggestion of looking into hiring a private driver/tour guide if you are looking to visit specific towns. Not only will it be less stressful if you don't have to drive, but you'll have a local who knows where they are going and speaks the language.
You definitely don't want a car in the major cities. There can be a lot of traffic and parking is difficult. Public transportation is easy to use and very reasonable.
"road signs are all in Polish". Actually that's in the US. Road signs are in English. In Poland as elsewhere in Europe they are using international road signs. You don't have to know language of the country you just have to know the road signs. If you do the drivers test in Europe and you don't know the road signs you won't pass the test. I noticed that quite many Americans don't know what these signs mean and despite that they drive on European roads.
Actually, although the road sign symbology is per international standards, the signage itself seems to be in Klingon...sorry Ilja, I meant Polish.