I have an MBP circa 2013 (e.g. 4gb RAM). I use it just about every day for ruby programming for work. Before I upgraded to Yosemite the platform was extremely stable and I never had it crash. After upgrading to Yosemite I have had a few crashes and maybe 5 or so Safari crashes. I do drive it pretty much to max frequently so I’ve been looking at the new MBP with 16gb RAM. That should solve all of the problems I would expect.
I use Safari, but I really don’t like it much, because it frequently crashes. Firefox never crashed that often, or even the dreaded I.E. My new MacBook Pro has Yosemite, but I haven’t used the MBP often enough to really get a feel for Yosemite.