BiggerPockets

Both.

Good renters would tend to hold back. Not just in winter, but after school starts for their kids. Same thing for selling a house. Volume slows with fewer buyers.
There remains a good stream of prosepective tenants, however, most of which are just a couple steps ahead of eviction. They never dry up.

Different places in the country have different trends. In general, you should buy in late fall, rehab during the winter and rent in the spring to early summer.
Buying in the late fall get you the best price for the property. People usually don't like to make big commitment right before Christmas. They need the money for presents, hosting, etc.
Most people try to stay away from remolding during the harsh months of the winter - That would give you an edge when shopping for contractors and professionals.
Most people start looking for a new place to buy or rent in the spring. They hope to move in the summer right before the new school year.

Depends upon where you are in the country and the economics of your area.

We are in a predominately retirement-based Florida area, so medical is the primary employer, followed by other services. Most are suffering.

Vacancies abound in the medical commercial areas, a sight unseen a few years ago. Foreclosures continue to rise but home prices have leveled off and do not seem to be dropping much if you can find a buyer.

For us, January - April is the best time to get lower to lower-middle income renters as tax returns are usually the basis of a new renters security deposits and full last and security deposits usually mean a fairly problem free tenant. We tend to try to manage our leases around this and adjust our rents to fill leases during this period.

There are some seasonal rentals in winter but not nearly as much as normal.

Summer is the worst for us, as economic activity is dead slow due to snowbirds being gone, and this is the period of our worst quality tenants and least activity in renting. Most service businesses are dead as well, so common to see layoffs during this period as well with service businesses.

Rents are way down from a few years ago and problem tenants are way up.

The quality of credit is almost non-existent as we have little high paying jobs so most tenants here live paycheck to paycheck or are recovering from some financial problem.

How long this pattern will last here is anybodies guess.