Generally, you want a fairly low heat and plenty of air movement. Which places a toaster oven with a convection fan at the top of the heap, imo. Air fryers tend not to be able to be set as low, but they’ll work, as would a full sized subsection oven (though ffs that’s a lot of energy used)

You can get by with a lidded pan and something to keep the sandwich off of the actual metal directly.

If you gotta use a microwave, try opening the sandwich, then wrapping it all in paper towels. It’s hit or miss, but it usually keeps the bread intact.

If you got it, sandwich press is best, if it’s fridge cold it’s probably best to wrap it in foil or something and don’t preheat the press, put it in cold, then once it feels pretty warm unwrap the foil give it a little toast. Doing it this way let’s it heat up but trap the moisture so it doesn’t dry out and then the final toasting stage stops it being flabby. Some cafes also do a microwave first stage and then sandwich press which I guess follows the same theory but for whatever reason, in my opinion that never works and it’ll always feel microwaved even if less so. Good method of you’re in a hurry though.

panini press

I know you asked for ways other than the microwave, but Id like to point out that sometimes the microwave can work well on leftovers(including sandwhiches) if you put in a little more effort than just tossing it in for 3-5 minutes and coming back to it being both scorched on the outside and cold on the inside.

2 different methods id suggest…

Remove the center of the sandwhich and microwave that for 1-3 minutes or until warm to hot then put it back in the bread and heat for a final 20-30 seconds.

Alternatively, I find some foods are heated more evenly if you cook them for 30-60 seconds, then let them rest for a minute, then repeat 2-4 times until the entire thing is hot. It gives the heat time to disperse instead of nuking some spots while leaving icicles elsewhere.

I like a reverse sear. Here’s the method:

Cook on a pan, medium low heat and flip often. Once the bread is at the preferred level of browning, cook it in a toaster oven (or a household range) at around 200-250F until the contents are warm. The time that takes depends on the sandwich and initial sear method, just check it plenty of times until you get a hang of it

There is no good way to reheat a sandwich… Eat it cold or throw it out.

Micro can work.

Open sandwich, separate ingredients at least a little.

Set power to 40%. Time @ 4:44.

Flip ingredients @ 2:22.

Lots of options here but my favorite is to use an elevated metal grate, as used for steaming, at the bottom of a pot, then put the sandwich on the grate. Put a few drops of water in the pot, cover it, and put it on low heat for as long as it takes, usually 5-10 minutes.

The low heat and extended time gives you a thorough heating all the way to the middle. No direct connect to the pot, so the bread doesn’t get burned.

Adjust the “few drops” of water up or down if the bread gets too dry or too soggy.