i am not a pro; however i can tell you that the SPF number just indicates how many hours of protection that you are going to have.
SPF 1 is equivalent to approx 20mins of protection. so, if you are using SPF130, it will be about 43hours of protection. However, if you sweat a lot, you just need to re-apply it few hours later. honestly, we really don't need that long of protection unless you are out there and stay under the sun all the time.. i.e construction worker and all.
if it's just for daily use, i use SPF50.. actually, normal days, SPF30 is sufficient for most OL work or just for school.
ok.. now moves onto PA factor. while SPF is for the hours of protection, which also protect us from UVB, PA factor is for UVA protection.
there are 3 types of UV rays from the sun. UVA, UVB and UVC. UVC will not reach the earth. UVB can be minimized by umbrella, shelter and all, UVA is able to penetrate through window, clothing, umbrella and etc. That's why we need to choose a sunblock that gives good UVA protection, which is with good PA factor.
PA factor comes with +. there are 3 + altogether. So far, 3 + are the highest protection in the market right now. I will usually buy sunblock with SPF50 PA+++
well, this is the info for now.. hope that this can give you a little information on sunblock and how to buy a better sunblock

good luck