First time we did ET work in 1988, we used 10 Holstein heifers, what a train wreck that was! They wouldn't try to have the calves, then some didn't want them, then they looked like skeletons, you couldn't feed them enough.
The Brahman X Holstein cross was a good idea if you're down south. It gives you the milk plus the ability to have a large calf without assistance. But like another poster mentioned, htey might be more difficult to sync and the disposition problems might not be so good. When I went to Central America with my ET guy in the early 90's they were milking Brahman X Holsteins, by hand in dairies. They were losing a milk hand or two a day, lol.
I'm sure it also depends on what kind of calves you're raising. If it were jerseys or maybe angus it might not matter about the size of the recip. But we have raised Simmi's and club calves so it matters a bunch to me that a cow can have a large calf. I've got a couple of 1800 recips. They are awesome. One had a 130 lb calf in 20 minutes. For me I would like to have as much Simmi or Gelbveih in my recips as possible and not as much angus or hereford simply because they can have larger calves and they milk so well. I only know one Simmi bull who's relatives have a particularly hard time calving and we stay away from those.
To me, fertility, milk, disposition, and the ability to calve unassisted are what we look for in a recip.
