I got sick of guesswork with ribs. The common misconception is that you can't temp ribs because they're too thin. You can. Temp in the middle of the rack between the bones. Use a good thin probe thermometer. I use the Thermapen.
180°-185° gives the perfect consistency for me. 190°-200° will get you into falling off the bone territory.
In my smoker at 300° I usually start temping at two and a half hours. Usually hits temp right around 3 hours. Then I wrap them and let them rest for 30-45 minutes.
Baby backs and spares are equally easy using this method. Any pit temp is fine too, though obviously the timing will change.
I struggled with ribs for years, never getting consistent results. Then I saw a post on here by Disco called "Ribs the way I like them", tried his method and boom. Consistent results time after time after time. No guessing, no voodoo, no BS. Just repeatable ribs done right every time.
Edit: didn't mean to Parrot SmokinAl, took me a while to type out my reply.