I consider myself lucky to have quite a number of local paths and trails to ride. One of the most popular is an MUP that follows the Rio Grand river and is pretty flat and fairly long, kind of crowded at times but it is a good scenic trail and pretty easy to do up to 20+ miles on. There are also quite a few neighborhood trails, although not as long, that are nicely paved and can be a bit more challenging as there are more hilly sections. Now on the flats we average 12 or so mph, but on the hilly neighbor hood trails we seem to be averaging about 9 mph (have to stop and start more on cross streets and such). Right now we have been mixing our rides, usually doing shorter rides on the neighborhood trails (6 to 10 miles) and longer rides on the MUP by the river 12 to 20 miles. What do you guys prefer as a work out, flats or hills?