Hi Saka and welcome to Wetpixel.
I have the Seacam housing and have used it on a few trips (Bahamas sharks, and Bali macro).
I love the housing of course. I can't think of too many differences between the two brands, as they are both ultra-high quality and both have nice viewfinder and port options.
It's hard for me to compare, as I've never dove the Subal housing, only "dry fired" it. If anything, I'd give the slight edge to Seacam because of their large Superdome, and slightly better viewfinder. They also offer a new "remote control" option, which is very cool for polecamming. The Seacam housing is very reliable, and if it's possible for an underwater housing, I'd call it idiot-proof.
I had a Tiger shark slam into mine last year. It rotated the dome port 90 degrees and knocked me over on the swim platform, but the housing and dome were totally unscathed. I don't think the same could be said for some other housing brands if they'd had to withstand a similar onslought.
Cheers
James