A flash, is a flash, is a flash, be it a studio strobe or a hot shoe speedlight.
Of course you may be using continuous studio lights.
Here's the deal. It is easier to learn to use strobed light with the camera and the light in manual modes. You can also produce more consistant results that way, and the best way to light people for portraiture is with the light
off of the camera (OCF, off camera flash),
In that case you don't need a camera makers hot shoe flash, you just need a hot shoe flash you cab set the power on manually, and a way to trigger it OCF. Of course for quality portraiture you will need several lights
For nighttime portraiture you still need to modify the light (much larger apparent light source) so you have nice soft light, and soft edged shadows, so again you need to OCF. Unless you're going for that hard, harsh, just one light on the camera hot shoe, amateurish look.
We are good for saving you some $$$'s, because the non-TTL 3rd party hot shoe strobes are not as expensive. So here are some you could consider that have good power ratings (GN number):
This flash has some automatic functions because of the thyristor it uses. I have 6 of these:
Vivitar 285HV Auto Professional Flash
in case you need TTL -
Vivitar DF383 Digital TTL Shoe Mount Power Zoom /Swivel /Bounce Auto-Focus Flash for Nikon TTL, Guide Number 45m (147')
Yongnuo Flash Speedlite Yn-460ii for Nikon Canon Pentax
Speedlite YN560 Flash for Canon, Nikon, Sony Cameras