Personally I look at what each party says, it’s manifesto and I decide which ONE suits my views. I don’t have a “second” choice as at that point I have already made a decision on what I want.
All this fudging and choosing somebody to fill your second choice just seems to me to be quite mad.
In this respect even under AV I would still only select one candidate as it is incomprehensible to me how I could also favour a second candidate but not as much? seems massively childish.
Once you have weighed up the pros and cons of each party you can only come to one decision on who you want to wield power on your behalf… seems black and white to me.