Try a lorry
If they're using the same bike, then they're using the same technology - so any difference must be found with the rider and not the bike. If both riders are equally sized then there's nothing else than rider differences to blame. If one rider is tall, and the other short, then who the bike fits best can also be an issue.
If you're 6ft and want a strong, fast bike that's good for freestyle and trails, try the Faction Zeitgeist. Its got 22" wheels, so it looks proportionally better for tall riders.
It depends on how tall you are and what your intended use is. Best advice is to get along to a bike store to try some out, if you're taller than the average rider you may want to look at a bmx cruiser too.
Suzuki V-strom, 650 or 1000. You can purchase a taller seat right from Suzuki, put on a set of bar risers and can even lower the pegs if needed.
Any Trails or Enduro style bike would be more comfortable for some one who is fairly tall.
Suzuki V-Strom
There is no best weight although it is a bit harder for a lighter rider, but as long as the rider is tall enough the suspension can and should be adjusted to the riders weight.
Rider Strong is 5' 8".
Dylan Rider is 173 cm.
Nancy Rider is 5' 3".
To me i like 110ccs but it differs around how tall and big you are