Yes. The brothers give off the following happiness values, but it's based on your pokemon's current happiness:
0-99 100-199 200+
younger brother +10 +3 +1
Older brother +5 +3 +1
as you can tell,. the younger brother gives more if your pokemon's happiness is pretty low from the start. so if your pokemon has a happiness of at least 100, just go with the younger brother, since he's cheaper.
which brother you get depends on the day: