It depends. The pre-Ai lens can be the old Sonnar-type, or the new Xenotar-type (same as AI and AIS versions). You can find out by checking the serial number: photosynthesis.co.nz/nikon/serialno.html#105
The Sonnar-type lens has smaller rear element; they also have a distinctly different design compared to newer Xenotar-type lenses.
Optical construction aside, there are more differences between the two designs. The Sonnar-type lens was only produced single-coated, with 6 or 9 (!) aperture blades. (I have both versions). The first Xenotar-type Nikkor-P 105/2.5 (s/n 407301 and up) was single-coated, and had 7 rounded aperture blades. The next one up was labeled Nikkor-P.C. 105/2.5, and was already multi-coated (an early version of NIC multocoating were used). The AI version had updated NIC (Nikon Integrated Coating) MC, still 7 rounded aperture blades. The subsequent AIS version had 7 straight aperture blades, and had NIC multi-coating. But that's not the end; in early 2000's, Nikon switched to another type of MC they named "SIC" (Super Integrated Coating); these were applied to AIS Nikkor 105/2.5 with serial numbers in the 103xxxx-105xxxx range (approximately; the 105,xxxx lens that I have already has SIC coatings on it; lenses earlier than 103xxxx may be iffy).
Hope that answers the technical part of your question. Now, what you will prefer for portraits is a totally different matter of personal taste. Me, I have most versions of this lens, from the very early 9-bladed Sonnar-type to the latest SIC-coated AIS version. They render images in a very different way. Modern MC versions are sharp, very contrasty, producing smooth background rendering and lots of "pop" or "3D" in the images. I like that. However, the early Sonnar-type lens makes nice, well-rounded portraits with beautiful color gradations and that somewhat vintage, characteristic Sonnar look that's simply missing from the newer (and, technically, better) AIS lens.
I took (and printed) many great shots with AI and AIS 105's... but my favorite portrait was shot with an old Sonnar-type lens.