Dormitory is easier at first.

But check the room, rent, rules, and location.

Some dorms are not comfortable.

I think dormitory is better when you first arrive.

Renting by yourself needs money, documents, guarantor, and Japanese communication. After you get used to Japan, moving out is easier.

Dorm is good at the beginning, but don’t decide only by “cheap”.

Check these before you say yes:

rent
utility cost
how many people share kitchen/bathroom
curfew or visitor rules
distance to work and station
can you move out later or not

Some dorms are fine, but some are old or too strict. If the rent is almost same as an apartment, I would rent by myself after a few months.

Also check if the dorm fee is taken from salary.

Sometimes “cheap dorm” becomes not cheap after utility fee, cleaning fee, Wi-Fi, bedding, etc.

If you care about privacy, apartment is better.

If you care about saving money and simple paperwork, dorm is better.

First 6 months dorm, then decide.

If you live in company dorm, moving job may also mean moving house.

Apartment is more free, but dorm is safer if you don’t know the city yet.

Check the contract first.

Some company dorms have rules like “you must leave soon after quitting job”.
So if the company is bad, housing also becomes a problem.

I stayed in company dorm first.

Good point was easy. I didn’t need to search apartment, make contract, buy fridge, washing machine, futon, etc. When I arrived in Japan, I was tired and didn’t understand many things, so dorm helped me.

But bad point was rules and privacy. In my dorm, kitchen and bathroom were shared. Some people didn’t clean after using. Also washing machine was always busy at night.

So my advice is: dorm is OK for first 3–6 months. During that time, learn the area, save money, and check apartment rent near your workplace.

But before you join, ask the company clearly:

private room or shared room?
total monthly cost?
photos of room/kitchen/toilet?
can I move out later?
what happens if I quit the job?

Don’t just ask “is dorm available?” Ask the real living condition.