Canon 135mmF2 usability with a Canon 7D?

[Daniel Browning]

usability of the Canon 135mm F2 with a crop body

I'm sure it's very usable on a crop body, though I've only used it on full frame.

if they have both, which one they reach for first?

It depends on the type of shot you're going for. Indoor headshots? 85mm. Outdoor ECUs? 135mm. Another factor to consider is that when framed the same, it's more difficult to nail focus on the 85mm than it is for the 135mm if both are wide open. But the 85mm can pull in more background and blur it, potentially making the composition more interesting than the smaller and more diffuse background of the 135.

I have a 24-70 and then splurged on a 24mm 1.4 and that is my favourite lens.

Welcome to the club. That's my favorite lens too. (Although I have to say that using it on a crop camera makes my heart break.)

I suppose I am working and saving towards a trinity of primes.

On crop I would go for the 85. On full frame, the 135.