Users of bivi bags and tarps and people who fabricate their own shelters from sticks, mosses and bracken look away now...... (This is about tents!)
These would be my criteria
1) I always look at the size of the porch first - can I cook in it safely in bad weather? Could I make brew without getting out of my sleeping bag? - It needs a fair amount of room to do this, but it just needs to be basic shelter. And its good for storing wet kit.
2) Next I'd look at the weight - the lighter the better, but not more than 2kg at the absolute most - with all the pegs/poles etc. But watch they dont save on weight by providing nasty bendy pegs and delicate poles. (Akto only uses 8 pegs and one pole which is one reason its quite light)
3) Id look at the quality of the poles. Akto poles are slinky and fit together easily. My "Millets" or whatever brand it is, Severn which I use for campsites (and which cost me £19) has poles which have poor aluminium connecting sleeves and the poles are liable to bend and flatten to extreme levels in strong winds - which I mitigate a bit by using extra pegging points and guy ropes, and by camping next to walls or hedges!. I'm expecting the thing to collapse on me at some point, though. Stormy nights can be quite exciting. I can get all my kit and the dog in it for an extended stay, though.
4) The groundsheet should be a nice all-round bathtub shape to keep out sogginess.
5) How quickly and easily can I get it up, and take it down again?(Oooh matron...)
I always have trouble with geodesic shapes and young boys gather around to laugh and point at my struggles and say things like "Canna ye put yer tent up, mister?". So simple one or two pole tents are for me.
6) In midge-infested areas, can I sit in the tent and look out through some nice mozzie netting whilst laughing at the pathetic attempts of the local insects to get at my delicate flesh for a blood-feast... until its time to go for a wee....