I would have to say the tibetan,they are more family orientated.Lhaso's are standoffish,nippy with children and very independant,if you like that sort of breed why not go for a shih-tzu,i have 2 of them and they are the most friendly,placid,loving dogs and they're always up for a cuddle :) Before i got my tzu's i was looking at lhaso's and saw alot of breeders,a few also had tzu's,as soon as i met one they stole my heart,i am so glad i brought my girls home,they are the light of my life and never give me any trouble,they are angels :D.Ofcourse the above descriptions are not set in stone you may find a lhaso who is the opposite of what i described,but in general this it what i found,or you may find a tzu who is unfriendly?Make sure you find a reputable breeder and they can advise you further.I must commend you on your taste you have picked a pair of cute breeds ;)
Please let me know if you have kids and how old they are?
If you need anymore info please dont hesitate to ask,or you can p.m me :)
christine