Phew where to start I can go on forever talking about hens
it sounds like you will have a blank page to start with so to speak. A little info and a few surgestions might help. The one important thing I've learnt in my poultry keeping experience is all hens have different personalities whatever the breed shape or size it's a 50/50 risk you might get a bad one.
Nearly all commercial hybrids are a 1st x with one parent being a RIR, Rhode island reds are fantastic egg layers but they are not the most sociable birds around and its common knowledge that they can be nasty. Personally I always buy birds in pairs of the same type. This has taught me that the personalities of each hen are very different. Some tame very easily others will always keep their distance. In my bunch at the moment I have 2 Ambers they are by far the friendliest. My Ambers are a RIR X white star they vary in colour from deep cream with Brown flecks to nearly white and have got very gentle personalities they lay creamy Brown good sized eggs once they get going. A close second is the copper head marans again a RIR x French marans lovely big back birds with shinning copper neck feathers with very different personalities. One has a not a care in the world attitude the other panics a bit and can be flighty. They lay wonderful dark reddish Brown eggs. Also in my bunch are 4 white leg horn x white stars these are full of personality fantastic layers of large white eggs, but not suitable for petting birds as they are flighty and very fast. Then come the Colombian black tails another RIR x i had a few problems with these 2 when the bluebell was around but there bad behaviour stoped once the bluebell was gone. they are good layers although 1 does like to brood for 10 days or so before giving up! Not bad for a hybrid. Then I have my broody a Gold Top she's beautiful, loving, and wonderful to own plus 1 other that I really have no idea of its parentage? A pure mongrel
Another breed to look at is the LS light sussex good all round birds, good egg layers but the down side is they don't take to confinement very well, they do much better on a large free range system.
A breed I am looking into at the moment is the Welsh black supplied by castlefarm poultry it's worth having a look at the website. What ever you decide my advice would be do some research and shop around, take your time and choose wisely, pay a bit extra for good birds it pays off in the long run. A final word if the hens you have now are vaccinated? Get new vaccinated birds. Nearly all pure bred hens are not vaccinated, so if there's anything in your ground vaccinated birds are ok with it good luck happy hen shopping