The round berkshire cycle way isn't bad in parts, tho some signs are missing or pointed in the wrong direction and most of it is quiet roads. Alternatively get an os map and works out some quiet routes, all will have hills in though.
Around Inkpen is fine, and combe gibbet and warbury hill are slow up and fast down.
You can go towards and over watership down, lots of nice realtively quiet routes there
There is also cycle route 4 which has nice oarts and follows the canal in places, not much use for a tike or tandem though
I mostly look at the map and follow quiet routes where possible.
James