Don't need to be a tamer to ride one....
I guess it depends on what you do mostly. I prefer my regular beetle because of it's built in backpack...I keep my Fire in the stable unless I am going out to do some hardcore mining.
For me, nothing beats having the regular beetle to carry an extra load for you
unless you are a miner and needing the 'portable forge' not really much other reason (can't remember 'attack' properties on a fire beetle)..otherwise, i'd go with the giant blue beetle, for the backpack feature as was previously stated