I own both the 105/2.5 AIS and 135/2.8. I find nothing to complain about with either. Nikkor - The Thousand and One Nights, Tale No.5 said regarding the 105/2.5 AI...
The lens also has characteristics of spherical aberration and coma. Basically close-range aberration variation is small, but at portrait distances the correction for aberration seems to be slightly insufficient. The insufficiency as far as spherical aberration in particular is what makes defocus background appeared beautiful. The aberration balance has been calculated carefully for use in portraits. When the aperture is open contrast is good, and delineation is soft.
In my tests of three of the Xenotar (modified Gauss) the three lenses achieved their sweet spot a little later than other Nikkor primes. Judging mostly on the center I called it at f/5.6. This agrees with 1001 and 1, Tale 5 and also with David Ruether who says of both the 105/2.5 Xenotar and 135/2.8 (Compact, AI, AIS, Maybe K), "performance declines at wide stops near minimum focus (both conditions together), otherwise this lens is excellent even wide open"
Since the 135/2.8 is a natural lens to use for portraits, tight head shots, it's quite possible that the same design philosophy of slightly soft at wide apertures and portrait distance informed the design of the 135/2.8. I've meant to test this once I got a D800 but I just shoot with the 135/2.8 and like it.
I prefer the 105/2.5 as I like the perspective I get better with 105 than 135. When the framing is the same I'll be standing a little closer and the closer distance produces the perspective. I like to say a lens "suggests" a perspective.
I don't find any bad habits with either my 105/2.5 AIS and 135/2.8 AIS. For focusing with live view I wish I hadn't give my 105/2.5 AI to pay a debt. After testing three 105/2.5 Xenotar types, N-C, AI and AIS I intended to keep both the AI and AIS. The N-C was sold but not delivered.
I'll throw one more lens in the discussion: the 105/2.8 AIS Micro-Nikkor. In my tests years ago my 105/2.8 AIS was right there with my 105/2.5(s) and it focuses down to 1:2 (half life size) so it can do double duty as a portrait and micro lens. With the PN-11 it achieves 1:1. With its CRC design it's probably wise to use a PK-12 and then PK-13 to achieve magnification ratio above 1:2 and until near 1:1 keeping the focus ring as near to minimum focus distance as possible.
Regarding the built in lens hoods on the 105/2.5 AIS and 135/2.8 AIS I've never had a problem with them. They are so wobbly, so bad that I've always used an HS-8 or HS-14 lens hood which offers better protection from stray light anyway.
I remember the first time I looked through a 105/2.5 Nikkor-P at Gayson's Camera. It just looked right. I immediately traded a 135/2.8 Nikkor-Q. The owner took the trade, 1 for 1. I'd owned the 135 for less than 24 hours. My preference for focal length is 105mm over 135mm.
That's my 2 cents on the subject...
Dave Hartman