I know that the swept wing decreases lift and the winglet increases lift. Is it better to have a winglet or a swept wing.
Both ideas are dealing with different physical phenomena, so there is no "better or worse" as they are, actually, sometime complementary.
Swept wing is used in high subsonic (Mach > 0.7) airplanes, and the idea is to reduce the effective incidence Mach on the airfoil, reducing the negative effect of compressibility on the drag.
However, the winglet tries to reduce the negative effect of having a finite wing as the air in the tail generates a vortex which increase resistance. In summary reduces what is called "induced drag".
So... low subsonic airplanes might have winglet and not a swept wing (notice that this one is trapezoidal):