We do both. Started with just spring, then bought some cows, then it just evolved. What most are saying is true. Higher prices in the spring for calves but somewhat higher costs to feed the lactating cow through the winter. Less flies, stress from heat with fall calvers. LESS PREDATORS for us here with fall calvers. Have next to no problems with the dang buzzards in the fall but they are a BIG problem in the spring.
Although we cull pretty heavy for breeding problems, I do like to be able to salvage a good cow, especially a first calf heifer, that doesn't get bred back, by switching her to the next calving group. They get a ONE TIME switch, but sometimes it just seems a bit too harsh to cull an otherwise good animal that missed getting bred. It is only a 6 month loss of time rather than a whole year if you calve once a year. If allowed to run with the bull all the time she would get bred a little later...so rather than have year round calving we regulate it and just switch them into the next group. We have culled alot of cows and lost 2 pastures due to sale of the land this year so have about 2/3 rds of the cows calving in the spring right now. Since we have more places to put cows out for spring grazing, will probably leave the balance this way. One of the places we lost we calved a big group of fall cows and it has hurt to have to shuffle cows around. We are also holding over some later spring born calves to sell a little heavier in early spring to try to not get kicked in the butt as prices kept dropping here this fall. We have the hay so will see if it pays....