First, some clarification on procedures and terms. Immigration and customs are two different things, although in the US people tend to say "customs" to mean both.
If you are flying nonstop from the US to Rome, on arrival you go through passport control (immigration), then pick up checked luggage, then go through customs. However, customs is just a matter of walking through the "Green Channel - Nothing To Declare" line. Unless you are stopped for additional screening (possible but rare), you're done. Immigration takes as long as it takes; if there are few people staffing the lines, or if several flights arrive at once, it will take much longer.
If you are arriving in Rome after a connection on one ticket through another Schengen country (for example, Chicago to Paris to Rome), then you go through immigration in Paris, but will not see your checked luggage there. On arrival in Rome there is no immigration (already done in Paris). You pick up your checked luggage in Rome and then go through customs. Again, customs is just a walk through; it's immigration that can take time.
If you are on separate tickets (highly NOT recommended) in the above scenario, you go through immigration in Paris, then pick up checked luggage and go through customs in Paris. You then make your way to your Paris to Rome flight, which is like a domestic flight in the US - no customs or immigration (of course, you still have to wait for checked luggage).
The reason you're getting various stories is that both immigration and waiting for checked luggage can be quick or slow, and can never be predicted in advance. All anyone can do is tell you their individual story - which may or may not match yours when you get there. You are also getting into personal preferences. Some people are highly sensitive to time spent waiting for luggage, and others are less so. You can't avoid waiting in immigration lines, but you can avoid waiting for luggage, so some like to control that aspect by not checking bags. Others just chalk it up as part of travel. And of course, those who've had a "nightmare" story, like luggage taking hours to show up, or not showing up at all, are going to feel much stronger than those who've never had a serious problem.
I think you have to balance everything and do what works for you. And if you need consolation about checking a bag, remember that this means you can bring all the sunscreen you want (pricey in Europe).
