One piece leathers probably give riders the best protection, although good quality textile clothing should be good enough. Two piece suits, whether textile or leather, are better if either the top and bottom can be zipped together, or if the jacket has a robust crotch strap.
We don’t accept kevlar jeans, as we don’t know how good they will be.
Both textile and leather suits should have CE armour in elbows and knees as a minimum. Shoulders, back and hip protection should also be better. There are also chest protectors available. Check your jacket has a CE marked back protector and not a piece of thin foam. Consider fitting a CE protector in the pocket, or using a separate back protector.
The European standard is EN1621-2 (Level 1 for regular use and Level 2 for sport/track).
Some leather suits are made from very thin leather, could be sheepskin. The quality of the stitching is also vital. Leather is not automatically better.
Here is some interesting general information and advice from Byson Leathers http://www.bysonleather.co.uk/BYSON%20LEATHER%20AboutLeathers.htm