My favourite has to be brotherhood or NCR, NCR do their best to help people and that is their main interest e.g. Take hoverdam to provide electricity to the waste. Brotherhood because they are a powerful group and I like how they scavenge old age technology. I dislike the enclave because I do not like what their entire group follows. But I do like their armour more the brotherhoods.
Moral of the story, don't snort RedBull... it's painful