what criteria to use with evolution choices

In the beginning of the game it could be worth to just evolve the one with highest cp and then use it for gym battles but later on it's better to evolve high IV and then invest dust. The high IV pokemon will serve you for a longer time than the one with low IV:s.

dratini 93IV and CP 478 (lvl 20)
charmander 91IV and CP466 (lvl 20)

If you are industrious enough to save dust and candy then
go for this >>> charmander 98IV and CP136 (lvl 6)

It depends on how rare the candy is, how much dust I'll save, whether I would want to further power up, what are the base stats like, how low the IV's are... Lots of variables.

One simple rule:
The higher you want to develope your pkm, the more important are IVs.

You should use CP-calc intensively until you get a good feeling for IV-Impact on CP and costs of leveling. So you can compare stardust, candy and final CP for all of your variants. Sometimes, you will want to level till 30, or you want to hit a frontier (2800CP+ Snorlax etc.) Sometimes, you just do not want to invest any dust, there IVs matter least, but level matters most. Sometimes candys or dust are an issue, sometimes less. Sometimes, your own trainer level will be the limit for leveling.
There are so many different attitudes to the game, so many different targets, so many different pkm, it is hard to give a handy rule of the thump.

depends.

level 20-28 is 58k dust and 52 candy
the level 20 will be about 2000 cp (powered up will be around 2800+ at level 28)
the level 28 will be about 2770 cp (if you used the dust and candy (the 52 to match dragonites) you could get this one to about level 33 - 3100+ cp

just hope you get the moveset you want...

I always have the same dilemma and I posted a similar question to this recently.
There are a few Pokemon where the best IV's (90%+) matter the most to me - based on personally favourites and those I know I want to invest dust in to use - so for me it's the normal likes of Snorlax (if I ever get one), Lapras + Dragonite. Then Gengar, Alakazam, + the 3 starters.
So if i looked at your list I'd invest in the 93iv Dratini and the 91iv Charmander. I'd still keep the 98iv Charmander - but I would probably look at the Charmeleon before this as he's gonna be a 2000+ Charizard... funnily enough I have exactly the same situation at the moment as this although my charmander is 91iv.
I did the same with a Machop recently - got a 95.6iv one around 650 but i caught a 73iv 883 so I evolved him first and got a 2093 Machamp with karate chop / cross chop which is what I was after .... although i've now caught a 956 Machop! lol

I used to look at CP only, but nowadays I only look at IV, since I have most pokemon at 90%+ IVs, I just want some perfect ones, or atleast with two maxed stats, even if its lvl 1 I would gladly power it up (given that it has a good moveset too, of course)