As others said, none of those bikes are worth upgrading to Ultegra/105. Depending on where you are you should easily be able to find an older used 105 bike in your price range and that would be a smarter way to spend your money. I would also skip disc brakes on bikes at that price level. If you are completely new to cycling then you probably don't know what you want or what kind of riding you will do so the best bet is get something used. If you buy a used bike for $600 with 105 you can probably sell it for close to what you paid in a year when you decide to upgrade. If you buy a new bike with Claris for $900 you will probably be lucky to get half that money back when you sell it. But as a new rider you really don't know how you like your bike to fit (i.e. what size is right for you), if you want a race bike, endurance, cross, gravel etc, if you want to be able to have wider tire, racks, fenders etc. Basically my point is that if you really get into riding you may decide a year later that you want a completely different bike