Best long range caliber?

I've always been told the heavier the round the more down range accuracy, I know that many variables come into play here but I guess the main this is, what do yall think is the most accurate long range pellet caliber? .177 .20 .22 .25 .30. I was told that .20 should be best since it has a flater trajectory than the other but still has some weight, but I've also herd ted say he likes his .30 cal since it bucks the winds better than his other calibers. I've thought about getting a good bench rest gun in my future for long range 100m shoots, but what's considered the best caliber in yalls opinion. I have a bsa r10 mk2 .22 on order but haven't got it in yet,
 
You have to consider what long range means in this conversation. At farther distances the bigger calibres carry better due to their heavier mass and of course resist wind better. The smaller ones slow down faster. And then there is retained energy to think about. You want enough energy to do some work once the pellet gets to the target. A .177 may only have a useful range of 75 yards where as a .30 can still be strong at 200 plus. It depends what you are trying to do.
 
For shooting pellets outdoors the 30 cal is the best long rang caliber. 30 caliber has won the AoA EBR 75 and 100 yard competitions the last 4 or 5 years. 30 cal bucks the wind better than .25 just like the heaver .25 .bucks the wind better than a 22.

You need a gun that can push the 44 grain 880+ fps. An 80 plus fpe airgun is going to have some recoil so for bench rest get an airgun with some weight. 30 cal Bobcats and Boss's are the guns that have dominated EBR at 75 and 100 yards.

Edit: Timmy Mac won with a 30 cal he built in 2014.
 
The original question is concerning "pellets". Slugs and bullets are a different animal (though I would love to have a gun set up for .257 one day). For me if I had to choose one calibre and long range target shooting/hunting was a big priority as well as reasonable cost and just general all around use I would say the .25 would be my choice. Especially the new 34 grain JSB's. Excellent long range pellet! 
 
For what it's worth,

I posed the same question to Martin at RAW prior to buying one of his rifles. Told him my main focus was 100 yard shooting and he recommended .30 cal. BUT not all rifles have the horsepower to sling 44-50gn pellets in their 860-880fps sweet spot, so .25 cal might be the better choice at lower energy, let's say 50-60 fpe. Get into the 40fpe range and .22 starts to look really good again.

This assumes we are talking pellets and unmodified rifles. That's a whole other topic.