As Martin says, it depends on your individual interests. On both sites, you don't have to pay to just browse what's available or even to search. In some spot checks for me, I found that newspapers.com had fewer years in most of the 'papers I'm interested in and it doesn't have one that BNA has at all. So if/when I have time to make intensive use of a sub, I'd go for BNA, which is a bit cheaper anyway (current offer excluded).
You may find one or both available free to residents at a library in your area, often even online, or you may have to go to the central one or archives/local studies/heritage centre, whatever it's called.
Both have free weekends (BNA through FindMyPast) from time to time, usually announced on this forum,
Find a Grave's Research Resources Forum and no doubt others. The trick is to keep a list of what you want to look up, and maybe do some free searches, ready for the great day.