FWIW mini-vs
will not be a very good match for campag ergos (or shimano STI models that were launched before 2008). A spongy brake with stuff-all running clearance will be the result. They work much better with later models of STI which have 'new super slr' (NSSLR) cable pull, which is longer.
Avid shortys and tektro oryx brakes are built very similarly, both in terms of geometry and construction. They also share a straddle that is a copy of shimano M-system from twenty-odd years ago, but in Avids and tektros the metal is not strong enough; these straddles break quite often. They also don't come in enough different lengths; you are better off fitting a traditional yoke and adjustable length straddle instead.
The current shorty models have a different looking arm but share the same geometry as the older ones which are virtually identical to oryx arms. There are a few differences though
1) the oryx arms are (IIRC) fractionally shorter
2) the avids come with decent brake blocks (and the tektros don't)
3) the tektros are made so that running a low straddle wire is slightly more awkward.
On the last point, the oryx arm with the straddle slot in has the slot in the wrong place; it needs to be deeper and with an improved entry radius, if the brake is to be used with a low straddle setting (which gives the highest MA). A few moments work with a file will sort this out.
If you
a) fit new brake cables (you would be amazed at how many people find their 'new brakes' work so much better when really it is new cables that are making the difference...…)
b) set the straddle cables low, and the arms wide (often extra washers are required to space the brake blocks out)
c) fit decent brake blocks
d) dismantle and grease the integral pivot bushings in the arms (which are usually bone-dry or partially seized)
(most of which you would do/have with new brakes anyway...) you may well find that the oryx brakes are not so bad after all. I think that shortys are better, but not that much better; the main advantage is that they are slightly easier to set up.
Avid ultimates are really meant for CX racers; you get to choose wide arm setting (low MA, large running clearance, for when it is muddy) or mid-arm setting (high MA, smaller running clearance, for when it is dry). The fancy pivot bearings give lower friction for longer, even when there is lots of mud about the place. You probably don't
need that per se, not on a touring bike. MA values are comparable with shortys.
Shimano BR-CX50/70 cantis are very good and (because they have slightly longer arms than shortys, I think,) are powerful enough that they can be used with NSSLR levers. With ergos or older STIs they are pretty powerful; again straddle height can be used to tune the brake power.
If you want a touring canti brake that is intrinsically a lot more powerful than most others, Pauls are worth a look. They are fiercely expensive though. A less expensive alternative are the cantis made by VO;
http://freshtripe.co.uk/velo-orange-grand-cru-zeste-cantilever-brake/even if set up badly (with a high straddle as per the photo), these brakes are pretty strong and if set up for maximum power (with a low straddle) they are amongst the most powerful brakes you can buy. They accept 'road' pattern inserts which gives you the widest choice of brake blocks.
Note that if planning to fit any long-arm canti, you need a bit more vertical clearance from the hanger; small frame sizes don't always offer enough clearance in this regard.
Note also that the range of MA adjustment in the long arm cantis is such that you can use them with ergo or 'old' STIs, as well as with newer NSSLR type STIs.
hth
cheers
