Both cars are great.
I think in most generally accepted qualitative ways the 3er is the better car. But seriously people, we're all driving around in awesome cars (be it a 128 or an M3) while billions on this planet don't even have indoor plumbing.
I worked very hard in school and later in my career to get to a place where I could afford my "cheap" BMW 128i. And even after owning it for 5 months, every time I push the start button I smile. Is the best car ever? I could care less because I'm happier than a pig in shit to be driving one. And if I was somehow disappointed for "only" driving a brand new 128i then that, my friends, would officially make me a spoiled brat.
So which is better? Who cares, be happy for your good fortune and enjoy the ride.