Ok none troll post this time.
Here is my amature take of J-20 vs PAK-FA
J-20 is definitively a more stealthy, simply it has a lot less surface protrusions, especially when it come to the under belly, I mean, seriously PAK-FA underside is almost identical to the Flanker jets. Just by that alone, defeats the whole purpose of stealth.
Both J-20 and PAK-FA have other problems that is unstealthy, just like J-20's canard, or the area between the carnard to the body, and the gaps on PAK-FA's engine intake from front, and it is huge exposed metal engine at the back. And both jet's round engine nozzle in the end, but I think this one will be different for the production version in 8 years.
When it come to maneuverability, J-20 wins hands down, better than F-22 or PAK-FA, simply because the canard+delta wing gives great AOA and low speed stability.
When it come to sensor and radar, both China and Russia will have comparable technology by the time they are both induct into service, maybe there is a chance China will be slightly ahead, however both will still be inferior to F-22. Unless US is too poor to upgrade the them when the time comes. And oh yes F-22 beats both in stealth aspect.
As for how much did J-20 got influenced from outside? I would say the influence is there, but only by concept and appearance, because there is nothing wrong by taking proven concepts, mash them together to make it better. And in the end, J-20 will be different enough to stand out from the crowd and make a good impact on the battlefield.
And I am proud for China's progress. I remember in the mid 1990s people were joking that Chinese can't make a decent Mig-21 clone... when they did that, people were joking the best fighter Chinese had was the 1960s era J-8, then they come up with J-10, and people said, so what? J-10 is 1990s technology. And Chinese respond by J-20, when people see J-20 they still say no way Chinese can produce this, it must be a copy/clone/technology demonstrator, in fact the initial online review by the western press is nothing short of racism, and once again I know they will be prove wrong,
However those naysayer do have one good point, because is so far the Chinese had made great effort mostly because of learning from existing technology, however they are now approaching world standard, so the question is can they build upon this concept and produce the next generation of hardware that is more advanced than US? Only time will tell to see if the Chinese system can produce true innovations, I see argument from both side and they are equal valid, so only time will tell.