I travelled both the routes during Aug 14th to 16, 2014. Better to take the route from Lucknow to Kanpur and then hit NH-2. Route via Bangarmau- Gursahaiganj- Chhibramau- Mainpuri was very bad and it was worse around Gursahaiganj and Chhibramau. You would take at least two hours more in addition to wear and tear, and mental exhaustion from constantly searching the road amongst the potholes.
This route has:
Lucknow Mauhan Hasanganj Rasulabad Marg and AH 1/NH 2
An excellent trip by road except the portion in Kanpur city where construction work is in progress. After Kanpur the journey was marvellous on the National Highway which is 6 lane. Returned via the same route. All facilities are available en route is excellent. You can eat and refresh yourself at the roadside dhabas. And there is always a nice feeling if you have your own car for driving.