No point in breaking light linkers. They don't do much damage, and they don't have good enough hit advantage for a good selection of manuals afterwards.
Heavy linkers are ridiculously easy to break if you say to yourself "if s/he does a heavy linker, I'm going to break". And heavy linkers allow the opponent to have a good selection of manuals afterward because of their hit advantage, so you should definitely not let the opponent get those free. If people let me do heavy linkers, I'm going to do nothing but Wulf's easy as hell manuals all day.
Medium linkers are... difficult (I don't bother)... It's technically a 50/50 guess at worst though, because if there's already been one hit, it can only be a medium or heavy after.
You MIGHT be able to break by looking at the hit animation, but it's one of those things where you need to have decided you're going to break it beforehand. Similar to manuals: you can't really distinguish between light and medium manuals fast enough if you decide you'll break either, but if you say to yourself "Ok, I'm going to look for a light manual animation, and if I see that, I break."
I call it "fuzzy breaking"- you can break with minimal risk of lockout if you know the animation down to the last detail, and you decide before hand that you're going to break that if you see it out of all the 3 different choices.