For best compatibility, I think Orbiter 2010 will suffice for you. Almost all older add-ons, including add-ons for Orbiter 2006 will run in Orbiter 2010. Orbiter 2010 also has some of the most popular add-ons.
However, if you want the latest and greatest Orbiter, that is Orbiter 2016. It has the best realism of simulation, and graphics till date. But, some of those previously mentioned popular add-ons have not been updated for Orbiter 2016, causing the issues like phasing into the ground and crashing and glitches. Otherwise, orbiter 2016 is just fine.
Welcome to Orbiter forum. How did you find Orbiter? After getting news of it going open source?