Although I haven't done 125th to LGA too many times (once to be exact) and maybe don't know what i'm talking about. But living in NYC, I have to say city bus service is only marginally faster than walking, except in the middle of the night. and bus riders do not exemplify civility, if crowded. and the stops are every freaking block! I would really think twice about it. for a few extra $$, a cab or Olympia is much much better, even if you don't have much luggage. Even though I 'm not a huge fan of public transport, for this trip I think taking the train is better. check the schedule careful to be on the express and not the local train - about 30 min difference. Also, some trains will have you switch in Stamford - i would try to get a direct express. At least there's a 99% chance that you will get into the city on time, and from Manhattan (wherever you are), it's a much easier to make you way to LGA (either bus, taxi or express bus). Also, parking fees in LGA are a bit steep for my taste ($30 1st day, and $15 thereafter - more than JFK!). There are some off-site lots, which run about $18/day, but you need to factor in extra time for transfer from them.