I have been through both situations - no low floor buses when DD was tiny. Used to have to hold DD under my armpit, load shopping up my arms, fold buggy (which WASN'T umbrella fold as I couldn't afford a Maclaren back then) and try to struglle on the bus with my bus ticket in my teeth. The one and only time someone offered to help me, they STOLE my entire week's worth of food shopping - I had no more money to replace it with, and I lost half a stone that week.
Now, low floor buses every 7 minutes on my local route (chose where I lived specifically because of the good bus routes, as I'll never drive because of my uncontrolled epilepsy). I have two prams. One is a cheap umbrella fold thingy from Mothercare (cost £35) that DS3 is very uncomfortable in, but is OK if I am just running errands or picking a FEW bits up. The other IS a fuck-off huge, practically unfoldable pram (to give an idea of the size - even 'folded' it doesn't fit into the boot of a Toyota Avensis, which has a cavernous boot). I got given it by a friend, for NOTHING. When I am doing a weeks shopping for 5 people - I HAVE to take the huge tank pram. It is the ONLY way I can cart enough food home to feed us all. I accept that it is fairly impractical for everyday bus use - but before DS3 was 6mo and able to go into a CHEAP (i.e. not Maclaren) umbrella fold pram - I had no choice but to use it every day, IN RUSH HOUR (shoot me now...) so that my dc could get to SCHOOL.
Oh - and I have two words for you all - MAC Major. When DS2 was non-walking at 3yo, a very tall 3yo, and was in a MAC Major - I was once asked to get off the bus for a wheelchair, and refused, as I was taking him to a hospital appointment. Why does an adult wheelchair user get priority over a child wheelchair user?? How many times did I get huffed at when the bus driver asked people that were already on the bus, with clearly mobile toddlers, to fold their prams, because my DS was in a pram too...NO IT IS GIVEN OUT BY THE WHEELCHAIR SERVICE, IT'S A WHEELCHAIR FOR SMALLER PEOPLE!!! (Forgive the shouting please)
Oh - and now that DS2 is out of the MAC Major, and it's just DS3 in his pram, if a wheelchair user is waiting, I take one of two actions depending on which pram I have - umbrella fold, I fold it, my big Tank thing (always FILLED with shopping), I get off and wait for the next bus 99% of the time.
HOWEVER - There is one situation where I just cannot get off. If I have been food shopping and have my DS2 with me, AND I have no more money left to pay for another bus fare for him - then I simply cannot get off and wait for the next bus, as I will not be able to pay AGAIN for DS2. And DS2, while he can walk short distances now, cannot walk all the way home. He still HAS disabilities, even though he may not appear to. So, on a very very few occasions, I HAVE looked like a total bitch, refusing to get off the bus for a wheelchair user (3 times in the last 8 months), but it is because of a combination of MY disability, my DS2's disabilities, having to do food shopping thus having my tank pram AND having no more money left in my purse.
I apologise if you are the wheelchair users that I have pissed off - but I have my own crosses to bear too!!