Can horses try more for different people?

Most certainly they have preferences for people. They'll also act differently depending on who is on their back and/or the skill level of that rider.

Quick example. I went to look at a couple horses to buy and my parents went along as several horses were for sale and they were looking too. Anyway, we stepped into the pasture and one of the mares took one look at my dad, fell in love and seperated him out from all of us and the other horses. She kept her body between my dad and everyone else up to and including their dog. Damndest thing I've seen, dad wanted her right then and there but she wasn't for sale. Three years later she came up for sale and dad bought her before they could finish giving her asking price . Why was she for sale? She was at her 3rd trainer and no one could get her to work for them. She was very indifferent towards people and only performed half heartedly though well trained. Dad hopped on her back and she came alive, had a huge motor and would kill herself for him.

I think so! Sometimes it's because of difference in level, difference in the way a person rides, and other reasons.

My friend and I switched horses one day, just to quickly go down a short trail. We had both been leasing for the same amount of time, about two or three months. Well, both horses acted differently and you could tell they both wanted THEIR rider back! That was a heck of a trail ride and I gladly hopped back on Skippy at the end of it.

I think it depends on the horse, but it clearly is possible. My gelding is very passionate about collaborating with me, but he turns into a very different - an extremely lazy one - horse, if any other rider mounts him, even if a very skilled and experienced one. He's just one of those who tend to bond with one person only and won't open up for others unless he trusts them to an extreme level. Which he doesn't.

How did you guess?!

Where bouts in scotland you from? I rarely see any fellow scots on HF!
And like most people have already said, a lot of horses can tend to favor a certain rider. It's happened with whisks a few times, I put it down to the fact she's had one rider for 10 years now as soon as anyone else gets on she starts acting like a turd, her only saving grace is that I intend to be her only rider for the rest of her life so i'm not overly concerned about it.

Aires prefers me over anyone else. He will do anything I ask of him, but can be stubborn as the day is long with anyone else up. It happens on the ground, too. He will be a complete brat for my friend and she'll text me to complain about him, so I'll show up the next day to give him what-for and he's an absolute angel for me, even though she swears up and down he was bulldozing into her and fidgety when tied.

LOL I know this story. For the very first time a few weeks ago I put a rank beginner on my mare that only I usually ride. We were in an arena so it was pretty safe. My girl first tried following me and when I shooed her away she wandered off and started trotting around as though she was loose.....completely ignoring the poor girl trying to stop her. What a little stinker. She is push button, mind reading in tune with me but with other people, if you don't earn her respect she will do whatever she wants. Even my poor farrier, if I am not around she will pull away from him and give him a rough time. All I have to do is be present and she is good as gold. She is smart. All the horses I have ever owned went better for me than most people, that is the fun of building a relationship with your own horse, but my current mare is particularly sensitive about needing "mommy".