My personal opinion is that Samsung makes cheap phones that break easily. The internal hardware is nice but I've never seen a phone screen break as easily as often as the Galaxy S3. I don't know anyone with a Galaxy S4, so I can't speak to that, but my experiences with the GS3 are enough to prevent me from ever buying a Samsung phone again - and I love Samsung, all my TV's and my washer and dryer are Samsung.
If you get their Nexus line it's not bad, but that's because Google calls the shots. My wife's Samsung Nexus holds up very solid and has been dropped quite a bit with no real damage done to it.
If you're getting an Android phone I think it's a mistake to get anything not branded 'Nexus.' Nexus is the line where Google calls the shots on the specs of the phone - Samsung, HTC, LG may make the phone, but Google designed it. It also has the pure, or original, version of Android on it; it's not all screwed up with HTC, LG, or Samsung's awful overlays on it. If you get a nexus phone you'll get updates to the OS almost immediately. If you get a non-nexus line you're at the mercy of the manufacturer and the service provider (Verizon, AT&T, Sprint, etc); if the phone didn't sell well you may never get an update, if Verizon has put it low on it's priority list you may get it 3 months after everyone else. Those are not concerns with Nexus branded phones. I'm not sure I'll ever buy another android phone again, but if I do it will only be a Nexus phone.
Everyone I know with a windows 8 phone loves it, but I would put a lot of time into playing with one before buying it. Their app market is not very good. Same with the new blackberries. They're both small markets where most of the userbase is biased, so I'm not sure how much weight you should give their current users
That's all I have to offer on it :\