(EDITED Robert, I was writing when you posted!! Slowwwww writer, me!!)
The choice of mast set up depends mainly on the purpose of the boat.
They both good and bad. Depends. Many people want one set up other want the other set up. At the end of the day, the choice depends on what the boat is meant for. (opinions like allways, are just an extra. experience should dictate what you want on your boat)
For Cruising and small boats a deck step makes more sense, as it is easier to remove and transport. Also cruising boats normally do not require mast bend features, because they're not racing, and do not require built in mast tunings. Most prodctions use deck step to avoid the water ingression, and to make the mast smaller to ferry with boat when new.
As we move towards larger boats, mast transportation issues do not make a difference because the mast is already so big that 9 feet more do not make a difference, and you'll allways need a crane anyway.
I have a keel step mast for several reasons. One of them is because of the races. We needed a stiffer set up, to allow more mast control.
It allows better sail shape, specially on the lower end of the mast, because it allows to bend better to flaten the sail.
Initially we were going to have 3 sets of spreaders, but because it affects rating, we went for 2 sets and profitted the rigidity of the keel mast.
I can modify mast/shroud tension while racing, by using a special hydraulic jack installed under the mast, and can move the mast up or down according to the needs. So it needs to be bellow decks for this. We change tension when beating or downwind. It has a "locked" position so I can cruise with the family, too.
When deciding the inside arrangment of my boat, I moved the front bulkhead backwards and installed the mast in the front head shower, so all water that gets in is going directly to the shower drain. Solved a big problem here!! My mast boot is there for looks.
We needed the rigidity of the set up and my cabin was properly reinforced around the cabin hole for this purpose.
Also if still have some time to change tack if a shroud fails, before the mast colapses.
here are a few photos of the thru deck and mast installation.
Bellow the thru deck and on the bottom the mast base box, underneath it the hydraulic jack.