Whew, you make me feel better about this being a long time decision and the two breeds you are more interested in. Sad to say but if you had asked your question 20 years ago I would have told you without batting an eye lash that the only dog you should consider would be a Lab. They were fabulous dogs but once they went up the ladder of one of the top 10 favorite dogs then the money making breeders jumped on the bandwagon and started pumping them out as fast as they could without any concern to temperment. Luckily the brittany never hit the top 10 list and someone can correct me here but the Boxer feel out of grace so for the most part you have breeders that love both of these dogs. I think again you really have to read why these dogs were breed and what is in their makeup. My father always said, "dogs are true to their breed if they had a good breeder and a good breeding program" meaning they won't deviate from the norm to much and will do what they were breed to do.
One suggestion I would have for you is to go to the many outstanding dog shows that New York has and go to the days that the breed you are interested in is showing. You can find the schedule on the internet. You will learn a lot being around breeders and people who love the breed. You also could hookup with Boxer Rescue or Brittany Rescue and they can give you a lot of great advise.
Also remember, with a larger dog you will have to take more walks morning (not me in the winter time

)and night and also find a place for them to run as they will need the excercise. They are not like a little dog that can happily live in a smaller area.
Thanks for letting me know you liked my post and that I didn't upset the applecart.