Google Maps says the down-around Lake Ontario thru Buffalo route is quicker (4hr 10m vs 4hr 45 mn). But then again you'll probably have less traffic and less chance of a border backup going up and around Lake Ontario. You'll have fewer tolls if you head north. I'd probably take the shorter route and pay the increased tolls, but I don't think it's a clear-cut decision.
If you do take the Buffalo route, call 1-800-715-6722, and hit 2 when it picks up to get the latest border delays to see if you want to divert from the Lewiston-Queenston Bridge to the Rainbow bridge - assuming you have a cell phone.