There are a few...
Apple is the refinement of tech, sometimes first, sometimes not, but always works with ease... they don't release something until it WORKS
Nokia still make arguably the toughest (without buying a tough phone like the CAT) phones going, also camera's = Incredaballs
Samsung pushes internal hardware the most, except the camera... LG I this is the other side of the Samsung coin though only of recent in the phone world
I need to say Sony because they have picked back up their game with some nice stuff and HTC because they constantly have good hardware and get no-where with it
If you are spending 500-700 (depending where your from) on a factory unlocked no contract phone, as in top end phone, you really cant go wrong... 5, 6 years into this smartphone war... everyone has cemented their design style, have found fans and as they get better and more companies pop up i'd say Samsung will loose some ground as will Apple... Apple are on their 7th generation handset, Samsung are on the 5th gen, Lumia (as I am calling the company for now) are on the 3rd.... just about, HTC are on their 2nd, LG just just dropped a hammer of a 3rd gen, Sony are on their 3rd... To be fair they are all good just to different people... I wish there was a Z2 WP, that monolith would look great with monochrome, I also want a high res LG WP Flex 8.1 .... just yes....
Last point, I think part of Apples' success is "the small phone" idea... if Samsung or HTC or anyone were to bring out a small version of each... not this cut back crap... Same spec, all of it... just one has a 5.5 and the other is 4.2 or even 5 and 4... Have it 1080p, tune the processor back from 1.7 to 1.4 for battery, not change the chip, same storage, same ram, same camera, same price, maybe 50 cheaper... Apple's business would get destroyed except for the fact they are now making a large phone...