If it comes down to burn the SGA would be superior in a solar burn scenario whilst thunderlord is better on arc burn modifiers. Both have their strengths and weaknesses, such as thunderlord has the hidden exotic perk where they have a chance to explode on a precision hit. SGA is good for supporting fire to keep the enemy at bay. In my personal opinion the only use I have had for SGA is Oracle destruction due to the almost unlimited ammo with the insane rate of fire. Thunderlord is better in terms of actually hitting and killing your target.