The honest comparison, including where wood is the better answer. Humidity, termites, coastal air and summer heat affect the two materials very differently.
The comparison that actually matters
Most steel against wood comparisons are written by someone who sells one of them. We make steel furniture, so take the following with that in mind, and note that we have included the cases where we think wood is the better choice.
The decision turns less on taste than on conditions. A wardrobe in a dry inland flat with air conditioning faces a different life from one in a coastal house that is shut up for three months of monsoon. Most of the real differences between the two materials only show up under the second set of conditions.
Humidity and the monsoon
Engineered wood is the material most affected by humid air. Particle board and MDF absorb moisture, swell at the edges, and do not return to their original dimensions when they dry. The first symptoms are doors that stop closing cleanly and edge banding that lifts. Once swelling has occurred it is permanent.
Solid timber handles humidity far better than board, but it moves seasonally, and a wardrobe built tight in the dry months can bind in the wet ones.
Steel does not absorb water at all, so nothing swells and nothing moves. The exposure for steel is different: it is rust, and rust only becomes a problem where the protective coating has been broken or was poor to begin with. An intact powder coated surface in a humid room is not at risk. A scratch through to bare metal, left in the same room, is.
Termites
This one is not a close call. Termites do not eat steel. In districts where infestation is common, a steel wardrobe removes a category of risk entirely rather than reducing it, and it does so without chemical treatment or periodic re-treatment.
It is worth being precise about the limit of that claim. A steel almirah is not termite proof storage for its contents: termites will reach paper and fabric inside through an unsealed joint as readily as anywhere else. What it removes is the risk of the furniture itself being destroyed.
Coastal air
Within a few kilometres of the sea, salt in the air accelerates corrosion considerably. This is the condition in which the quality of a steel unit's coating stops being a detail and becomes the whole decision. A well pretreated, powder coated unit performs well. A cheaply finished one will show rust at the edges within a couple of seasons, and far faster than it would inland.
If you are buying steel for a coastal location, inspect the finish on the hidden surfaces and the folded edges, and keep the unit off the floor where salt laden water collects.
Heat and sunlight
Steel conducts heat, so a unit in direct afternoon sun will be warm to the touch in a way wood will not. This is a comfort point rather than a durability one, and it is easily dealt with by not siting the wardrobe against a wall that takes direct sun. Conversely, steel is unaffected by the dimensional changes that repeated heating and cooling cause in timber.
Where wood is the better answer
Three cases, and they are common ones. If the wardrobe must be built into an irregular alcove or run floor to ceiling against uneven walls, carpentry fits a space that factory made steel cannot. If the room's character depends on timber, no finish on steel will substitute for it honestly. And if the piece is expected to be modified, extended or refitted by a carpenter later, wood accommodates that and steel does not.
Steel is the better answer where the priorities are a long service life with little maintenance, resistance to humidity and termites, lockable storage, and predictable cost.
What to check, whichever you choose
For wood, ask what the core material is rather than what the surface looks like, and treat any unsealed edge as the point where moisture will enter. For steel, ask about the grade of sheet and the coating process, and inspect the surfaces that were not meant to be inspected.
We build the SECUREX range from CRCA cold rolled steel with a powder coated finish at our own unit at Kantabanji, Balangir, Odisha. If you want to talk through a particular room and its conditions before deciding either way, we are happy to do that, including when the answer is carpentry.