I've not bought beer to bring home in over two years now. Never really cared much for what BMC produced. Never tried Yeungling so I can't comment on their brews, but I'm not inclined to buy any to find out. I used to buy Guinness, Murphy's, Boddington's, and a couple of Sam Adams beers when I was buying. Sam Adams was meh most of the time (rarely had more than one). The others were bought only so often since they were more $$ for the amount you got. I would always go for the larger cans (with the nitrogen inside).
I won't begrudge a smaller brewery their success. IMO, any that can take market share away from BMC at least deserves respect, even if you don't purchase their products. That being said, I really don't have much respect for Sam Adams anymore.
When I go to a restaurant/pub/etc. I ask what's on tap. If there's something that sounds good, I'll get a sample first (if possible) and then order a pint accordingly. Unless I already know the brew is at least decent to drink. That being said, it's so easy to go to places that simply don't know how to properly dispense a style. Putting it on the wrong gas system can also completely change a brew. I had some Sam Smith where it was on nitrogen. I then had the same brew (at another place) that was on CO2. VERY different in the glass. I now also make it a point to ask what a place has on nitro.
BTW, there is a place in Portsmouth, NH that has really, really good Guinness. They clean the lines with each keg change (or at least they did the last time I went there) and have a rather high keg turnover. Several of the taps are dedicated to Guinness (or were). I need to get the name of the place so that I can swing in next time I go through that area.
They also had a pretty good Ruben (more traditional, so done up right).