Hi Paul!
Before we can give advice I suppose you should first tell us, what you mostly shoot.
But my first impression:
From your post I read that you don't need the reach of 300 mm FL.
If you still need or want up to about 300 mm, personally I'd just keep the 70-300L, because it's one of the best tele zooms Canon ever made.
If you for example change to the EF 70-300mm II USM you will not gain so much advantages in size, weight and return of money,
but you will lose a lot in built quality, color, contrast and so on.
For the lenses you mentioned:
The 135L is great portrait lens on FF, if you can get enough space between you and subject. On crop you'll get a decent tele.
Try that FL out with your zoom, if you like it or not.
The 100/2 or 85/1.8 are nice small and cheap lenses, but color and contrast don't pop IMO and they have some CA, that needs to be corrected.
I own the 85, but I would sell it in a heartbeat if Canon made a Mark II of it.
If you need more advice please tell us a bit more about your preferences.
Edit:
I really like the reviews from
Dustin Abbott and I just read from him about the 70-300L:
Dustin Abbott said:
Although I no longer own it, I highly recommend the Canon EF 70-300mm f/4-5.6L IS USM Lens: You can read my review
here: I really love this lens. It is fairly heavy, but is nicely compact and travels nicely. It is built like a tank, has great sharpness and color, and is very consistent throughout its focal length. This is one of Canon’s hidden gems, and rewards every one who owns it. I had a hard time parting with mine…
He replaced it with the 100-400LII.