As they themselves admitted they were like both sides of same coin, with their main character traits remains same for both of them.
They both are equally bad and equally evil, no one is less than other.
BUT,
there is difference in portraying their character or behavior.
Kish is very short tempered and once she gets into defend or anger mode she gets carried away with having no control over herself.
I think Mandy has control over her anger and the things what she is doing in each and every step of her.
For example,
1. In Hotel task:
Kish failed to differentiate between the task and getting to personal level. so she ended up in spitting in food, which is her way of showing her frustration and anger. Mandy handled the task within limit by hitting on her weak point to hurt her ego, kind of mind game rather not doing any physical harm. It was win-win situation for Mandy. Even if Kish does that task successfully or failed also somehow Mandy is the winner, which we saw.
2. In Highway task:
At first, Mandy in order to irritate Kish and to defend herself from the water thrown by Kish's team she took some of Kish's cloths and tried to use it. But when Kish and her team pointed out it is personal belongings she can't use it, she slightly took back her move and silently dropped that idea. Later when Prince gave Mandy's cloth to Kish, she just with her anger took all her frustration on Mandy's cloth's by spoiling it, which was absolutely not necessary at that point of time, as it was the other team's job to irritate them not otherwise. Kish just carried away with her anger and frustration without thinking. But later Mandy(may be after thinking for some time) can with set of cloths and showed that she didn't spoil hers but indeed Kish spoiled hers. Though Kish argued that she spoiled her shawl, its like Kish spoiled more cloths of Mandy than the other. So, even though Mandy started this personal attack she some how did damage control and came out of that, but Kish's action at that point was not all necessary and the hyper actions are not all necessary which made to look Kish evil.
Even though both Mandy and Kish are strong and are at same place in this race, can see a difference how they reached to this place. Kish surely using her two loyal people where as Mandy is playing single handy. Even if both of them reach the finale also, i think it will be like Kish is the one with some much efforts, shouting, bullying, taunting(spoiled her image) etc reached the finale whereas Mandy will be like effortlessly reaching the finale as she mainly playing mind game rather than grouping and shouting as vamp.
And, one more point of Kish is her habit of imitating others, its highly irritating to watch. Many times she did imitated Mandy even in WOW episodes also, during serious discussion also. its showing only her frustration on other person, but annoying to watch it.
Mandy, surely is a double trouble for HMs, it may be fun to watch, but to HMs might be going through tough time. But again its only in the show and its wining, in real life this situations will not happen as we will tend to move away from people whom we are not comfortable with.
At this point, i prefer Mandy over Kish.
Its not about supporting foreign fair skin as many mentioned in this forum, least bothered about their physical appearance.