I don't enjoy using any form of public transport. But buses are especially awful for me, because you have to share them with all sorts of strangers. There's gum under the seats, on the poles that you have to hold, and they are dirty. I hate them, so I only really use them when I have absolutely no other choice. So I prefer to go with the pay as you go option, rather than getting a pass.
I don't think I've ever paid for a one way bus pass in well over 10 years. I can't even remember if we had to pay the bus driver directly or go to some cashier to purchase a pass. I would much rather have all buses require people to purchase their passes elsewhere before getting on the bus though since that seems like it would really slow the bus transits down if they had to keep stopping and waiting for several people to pay on the spot. I have ridden the local RTA here in Cleveland though in recent years, which includes both buses and trains - and it's all automated for purchasing passes. There are large self service machines which take cash or credit cards and you can purchase all day passes for only $5, which is what I do. We've only used these though when we were going to several events and bar hopping throughout the day - $5 is way cheaper than paying for several taxi rides, and much cheaper than driving yourself and paying for parking several times, not to mention risking getting a DUI.
Bus pass, for sure. On top of costs being lower, bus passes speed up the process of getting on the bus significantly. I hate rummaging through my wallet for money.
Pay as you go, because I don't use the bus that often, but whenever I run into months where I'm going somewhere regularly I grab a pass, no questions asked. The savings are significant. It's also much handier than having to deal with tokens or change or whatnot. When I was in college my school had a deal with the local bus company that netted every student free, unlimited use of the bus, so long as you had your student ID on you. Those were good times.