In a comparison for instructional purposes only, the Russian T-50 is a sleek-looking fighter that is not very stealthy.
From my August 21, 2011 post:
Russian T-50 easy, medium, and hard fixes (topside)
China's J-20 Mighty Dragon stealth fighter
J-20 Mighty Dragon has no gaps between rear part of engines and fuselage. Notice the frameless one-piece bubble canopy. The continuous-curvature upper-body design of the J-20 is obvious to an untrained eye.
Russian T-50 or Pak-Fa "stealth" fighter
The first of many non-stealthy features, which are immediately noticeable about the Russian T-50, is the metal-framed cockpit canopy. Also, the protruding IRST probe in front of the cockpit needs to be recessed.
Thirdly, the gaps between the engines need to be filled to eliminate a stronger radar echo. Fourthly, unlike the J-20, there is no RAM coating over the gleaming Russian T-50 engines on the entire exposed upper-body surface. The T-50 designers may have to resolve cooling issues with its engines if they are covered with RAM material.
The fifth problem with the top-side design of the T-50 is the lack of continuous-curvature. On the Chinese J-20, there is a nice round curve to the entire upper-body fuselage. On the Russian T-50, there are sharp and oblique angles, especially behind the cockpit. The Russians need to obtain a supercomputer and fix the design problem.
[Note: Thank you to "MwRYum" for the J-20 pictures and Aimarraul for the Russian T-50 pictures.]
This is a clinical and objective post to contrast and compare stealth design features. This is not a "versus" comparison. If Sukhoi doesn't like what I'm pointing out, they should fix the problems.