Question about Pittsburgh neighborhoods?

i've moved to pittsburgh for a job a few weeks ago, but still haven't found a great place yet. what are some decent, middle cl, neighborhoods that a 28 year old single guy would enjoy living in? i'm looking for a 3 br house, rather than an apt or condo. someone suggested arlington to me. is that a nice area? what about carrick? someone first suggested negley/shady side, but i didn't think it was very nice when i went there to check it out. i liked mt. washington, but it was a bit hard to get to work downtown from there since the parking near the incline is poor. i was told allentown.arlington had a train within walking distance and that would be ideal for me. can anyone suggest any other place? what are brentwood and greentree like?