What exactly is the difference between a Master Sergeant and a 1st Sergeant? Is one technically higher than the other?

yes, they get paid the same as a E8, but 1SG is a position of leadership like the CO, so yes a 1SG outranks a MSG.

It's kinda like SPC. And CPL.

One usually is an office worker while the other is not. The 1st Sgt is usually out with the company. While the MSG is in an office doing all the paper work or with the Cpt or another officer.

Both are Pay grade E-8. The First Sergeant is a Leadership position at the company level. Master Sargeants are generally more staff related position. The MSG may be senior NCO like an Operatons Sergeant in a Detachment or Battalion or higher Staff section. Once a First Sergeant moves out of the position he becomes a master sergeant. There is a similar situation with Sergeant Majors. There are Command Sergeant Majors and Sergeant Majors. The CSM is a command position. Both are the right hands of their respective commander and generally speak with the authority of the commander.

A First Sargent runs the Company, and is the Senior Enlisted Advisor to the Company Commander. A Master Sargent might be in charge of one of the Battalion's "S" sections, or for example When I was stationed at Fort Lee as an instructor, The Petroleum Supply Specalist School had a Sargent Major, and a Master Sargent as his second.

Similar to what has already been said the same difference as a SPC and a CPL only at a higher level. The biggest difference is that as a CPL, the Department of the Army can appoint you the rank of CPL which you would not lose unless you are punished and go back to being a SPC, where as a MSG when appointed to the rank and position of 1SG and they finish that assignment and move on to another unit they go back automatically to being a MSG. There isn't a permanent assignment to being a 1SG. Each unit they go to has to appoint them to the position. Also a SFC Promotable can be "frocked" to the position and wear the rank of a 1SG without the pay of an E-8 but all the duties and responsibilities of the position and the rank attached to it.

Your curiosity is not without merit. However, you may find your answer locally from your unit and within your NCO chain.

I have a bit to add myself, Special Forces, Special Mission Units & Special Operations work at a different structure. Companys are managed by a SGM and Team Sergeants & Team Leaders are a MSG. There are very few 1SG slots in such units and are assigned at a Detachment level or at a Special Warfare School with the 1SG duties. NCOIC are a SGM position. The 1SG are considered staff position and a MSG is operational. The CSM positions is only at Detachment or Group positions. However, promotion wise the 1SG has higher considerations at promotion boards. Most MSGs prefer to remain on teams which the slot for 1SG is a ticket puncher to CSM. That was more or less the structure in my day but things change. Most of which I believe is the same today.

Command authority

A Master Sergeant is an E-8 and always will be; despite their role within a unit. While the First Sergeant Role is and E-8 position, it may be filled by someone of a lower rank. As an E-6 (Staff Sergeant) I served as the Company First Sergeant when my First Sergeant allowed all of the Comapny's E-7 take leave at the same time along with himself. I also served as Company First Sergeant as an E-7 (Sergeant First Class) when my First Sergeant was away at First Sergeants School. Both were temporary assignments of course. Technically, the First Sergeant Position is above the Master Sergeant within the company. But a Temporary First Sergeant better beware if he/she pushes a Master Sergeant around with her/his temporary position.