Is calling a MSG in the Army “Top” appropriate or only exclusively used for a 1SG?

I was a SSG in one unit. I was in the Detachment Sergeant spot. That is the spot for the Senior Enlisted Advisor to the Commander. I was called "Top" from time to time. It's unit depending. If the MSG is the Top Kick in the unit....then they could be called "Top" if they allow it.

I think some of these nicknames come from WWII. The Company Commander, even though he was in his 20's, was the Old Man. The First Sergeant was the Top Kick. A second lieutenant was a Louie. None of these is probably an appropriate term for direct address.

US Navy has Master Chief for E-9

It never bothered me. I was the acting BN and BDE CSM as a MSG for several months at a time multiple times.

Call'em first shirt or sleeve. Top kick is always a good one. The Master Sergeant who ran the turret shop, Had been a Major in Viet Nam and reverted. I just called him Sir.

I have always called my 1SG—or any 1SG—Top. I have never met a 1SG who didn’t want to be called Top.

I get called Top on occasion; not sure why. My title is SGT and not Top or Master Sergeant

There’s MANY ways this could be answered. From what I’ve seen in my career it’s ALL over the place. Many of the units I’ve been in or associated with is 1SG is 1SG, MSG is Top, but many 1SG’s usually have been MSG’s and like the “nick name” Top. Because I was in units that I’ve seen it both ways, it’s usually good to just ask when you start interactions with them. I was an E-7 but was interm 1SG until the new 1SG was brought in, many called me Top just because of the position. But between MSG and 1SG it’s the same darn rank, it’s just a position, no one should get all bent because someone “called” you by your rank. If ya prefer Top, NP, if ya prefer 1SG, so be it.
Just my two pennies for the day!!

Might do to understand the history of "top sergeant" aka "first Sergeant"...

No you should not call a MSG top That’s only for 1Sgt
My troops called me Boss I was ok with that
I see some 1st Sgt responded they don’t like it the phase Top
These are Top’s are up tight and are driven by power not the pursuit of the troops

If you had a Jewish 1st Sergeant, would you call him "dredle"?

I’ve always called my 1SG Top.

The first Sgt was the only one I ever called Top. The others I called by their rank.

Personally, I'm with @1SG Anonymous on this one. I call 1SG that I respect Top (unless they tell me not to), but I also refer to MSG as "Master Sergeant" or "Mass-Sarn't." To me, it's a respect thing. If I dont like you, you get no familiarity with me, and you'll only get the stone cold, half-hearted addresses and responses out of me. If I respect you, or I like you, you'll usually get something a little more familiar or more akin to camaraderie from me.

But the caveat to that is that of I am going to address you formally by rank, I would expect the same. If I call you "Top," I got no problems with P, P-A, Petey, Tony, Petri, or anything else. But if you demand a formal address because "oh, I have a rank and I earned it," then all is fair in love and war, I have one of them rank patches too, and I earned it. You may address me accordingly.

I call them by either Master Sergeant and 1st Sergeant. I called very few as Top!

Myself it’s to each it’s own my MSG in my company I address him by his full rank because of respect master sergeant. I hate addressing e5–e8 as sergeant. But my 1sg I say first sergeant my other e8 it’s hey master sergeant ( name)

well msg usually get more respect

That's mostly reserved for 1SG's. BUT, If the MSG is the SENIOR NCO in the Company, then it would apply UNLESS they CURSE you out for you calling them that. You might get a better answer if you do a correspondence course on Military Customs and Courtesy.

Military courtesy prevails. 1SG.

Not as a formal address to the senior enlisted adviser is it appropriate. We are called by rank just as you.

To me, "TOP" referred to the First Sergeant. He is the TOP soldier in that unit. I have never heard a Master Sergeant referred to as TOP, I retired in 2009 and don't know what is happening on active duty today.