Command
Take the command whilst it is offered.
Once you have some command time of EFIS jets, you are employable for both left and right seats down the track. If things go pear shaped - all of a sudden you have double the jobs available as opposed to just the right side of the plane. Demonstrated ability in addition to the requirements for applying for other jobs should you need to move on - along with the responsibility and job satisfaction of actually doing the job in command.
You can have my job if you like - been sitting as an FO for 13 years with my airline - patiently waiting for the first opportunity for a command, whilst continually trying to improve myself. Looks like it might be another 10-20 years or even possibly out of a job soon depending on which way the company turns.
So - swap? You have my 747-400 right seat......I'll do the "Bambi Jet" left seat......even throw a box of chocolates in for you?
In any case - whatever you do - make the best decision you can at the time and do not look back. Keep going - no regrets and make what you are doing enjoyable in the good times and the bad.
Good luck