Great question with a difficult answer for me because I have many favorites. I like doing loop rides, so here are two of my favs based on my eastside location at Camino Seco and Wrightstown:
1) South on Camino Seco, to Old Spanish Trail to Saguaro NP E. North on Freeman to Speedway, Wentworth, Ft. Lowell to Soldier Trail. N to Snyder, then west to Harrison or Bear Canyon, south to Tanque Verde then Pantano and home. About 30 miles. Low traffic, nice scenery, some climbing.
2) South to Escalante then to Aviation Bikeway, into downtown, over to Santa Cruz path, north to Rillito (or further, then back) east on Rillito to Craycroft, south to Pima, east to Tanque Verde to Pantano and home. Anywhere from 45 to 50+ miles. Low traffic, changing urban environment.

3wheeler Yeah. =)

For convenient sport/rec/training within the city, Broadway E/W/W/E early weekend mornings, back and forth, until you are spent, is great. Same goes for Speedway to a lesser extent. You  might feel like you own the city, those rides.

Outside the city, Mt. Hopkins Road up to the rest facility at the base near hike trailhead to Elephant Head ( just before things get really bad to impossible for cyclists). It’s paved, lengthy, rolling and quiet. Don’t tell.

Nice workout right out of downtown is a climb up A Mountain. Before 9am the gate is down for autos.

#1. Sonoita to Parker Canyon Lake and back through Elgin. Very little vehicle traffic, high altitude, beautiful scenery and a good workout too.
#2. Mt. Lemmon, when it is not windy. Smooth road, steady grade, great for interval and high altitude training.

1.  Kitt Peak: way more interesting than Lemmon (which is frankly boring) both on the ascent and descent, and  much less traffic.
2.  The loop through Saguaro Nat’l Park East.
3.  Picture Rocks through Saguaro Nat’l Park West to McCain Loop via Sandario and Kinney, then over Gates Pass headed East, followed by a descent into Tucson.
4.  The ride up and down Madera Canyon.