This is not an easy question. I have answered it, in ways, before. I have a fair few breeds of bird and I am not sure I could say I have a favorite because I like different things about different birds. That said...
Easter Eggers: I have only four of these, from 
TSC, and I love them very much. They are outgoing birds, forage well, are friendly and lay fairly well. I think if I could only have one type of bird it would be these.
Welsummer: This is another breed that I like. Just like my EE's they are friendly, decent layers but not as good as the EE's and forage well. However, mine have proven not to be as hardy. I have lost a few over the past year and they are only going into their second season. That could be poor stock and not an issue with the breed itself, in fact I am sure that is what it likely is (all of my birds are simply hatchery stock). Anyway, I think I like this almost as well as the EE's
Buff Orpingtons: These were my first birds and they are very, very friendly. I mean they follow me around the yard like dogs. They squawk if I forget to let them free range when I get home. They are okay layers at best. Oh, and they eat like a horse! If you want to save money on food then these are not for you. These are a very close third, simply because I like how they act.
Barred Rock: I only have one so take it for what it is worth. She is a very nosy chicken who is always checking out what the other birds are doing (and the dogs and the people too). She lays okay and is quite friendly. Small and seems to not eat as much as the other birds. I'd like to give more of these a go in the future.
Rhode Island Red: These are good working birds. They lay very well, are not flightly but are not overly friendly. They eat a moderate amount compared to my larger Orps but about average compared to everything else, I'd suppose. Not only do they lay well, they lay all year. Maybe they take a few weeks here and there but these are the birds that give me eggs in the winter. If my goal was egg, these would be my go to.
Black Australorp: These birds are about on par with my RIR's in terms of temperament. That is to say, they are not flightly or skittish but not really friendly either. They lay better than the orps but not as well as the RIR's. I could take these or leave them.
Blue Ameraucana: These birds are so very pretty! My Roo is very tolerant of humans and dogs. Never once has he charged or spurred (knock wood). The ladies are very hit and miss though! A few are very skittish, a few are fairly friendly and a few are like "look but don't touch". They are okay layers. I have one that lays in a clay pot on my porch about 4 times a week. I am not sure how I feel about getting these. Very pretty birds that lay nice eggs but hit and miss on the personality. 
Light Brahma: These birds are quite friendly but mine have proven to not be very hardy. Poor layers and they tend to get picked on once I let them out into the general population. I have one rooster and he pretends to be friendly but he is sneaky! I'd not get these again even if they are pretty birds.
Brown Leghorns: These birds are insane! Super flighty, not friendly at all. I can not get within 5 feet of them without they freaking out and flying away to the other side of the yard...lol. They lay well but their eggs are much, much smaller than I was expecting. I'd call them a medium to small. They are entertaining but I'd not get these again either. 
OEGB: I mean, these are really my favorite but as much as I love my birds I like eggs too so I could not keep just these! Mine don't lay well and the eggs are very tiny--lol. But you want a bird with loads of personality, look no further. I hate that they are straight run only because I always end up with half roos and once their switch flips they are brutal with one another! You have to get them separated quickly! I mean, I have other roos on the property and they will spar a bit if they wonder into the wrong spot but OEGB will run an acre to try to kill the other...Had to get rid off 5 of them right quick! My favorite bird of all is my OEGB roo though! Not human aggressive at all. Will take on the turkey though...
Anyway, that has been my experience with my birds. I am sure it comes down to loads of factors. Where you get the birds/blood line, how they are raised, individual personality and much more. But all in all I guess I'd say OEGB are my favorite and EE's are my favorite if eggs are brought into the equation (and for me they are).