On a crop body it is a great portrait lens , a bit soft at 1.8 but gets really sharp by F4-5.6 . At 1.8 and bump the ISO up you can get some nice low light stuff out of this lens

Primes are almost always sharper than zooms. This is because the optical formula for primes is much simpler and being of fixed focal length, it is much easier for lens manufacturers to come up with a sharp prime lenses than equally sharp zooms. There is no mechanism to alter the focal length - therefore the red, blue and green (RGB) color elements of the light will be more tightly focused onto your sensor plane.

Furthermore, the simplicty of prime optics allow manufacturers to design primes with much larger apertures - as large as f/1.0 or f/1.2. Zooms typically have a maximum aperture of f/2.8; except for the recently introduced Sigma 18-35mm f/1.8 DC HSM which is rather heavy and expensive for its rather short focal range.

You get to enjoy a shallower depth-of-field with the EF 50mm f/1.8 at larger apertures which also means the background will be nicely blurred out. The catch is that on an APS-C format body like your EOS 1100D your field-of-view will be similar to a 80mm lens on a full frame dSLR or 35mm film SLR.

If you're planning on buying the EF 50mm f/1.8, wait for the new EF 50mm f/1.8 STM to become widely available. It replaces the old EF 50mm f/1.8 II and should cost just a bit more than the EF 50mm f/1.8 II.

Another exceptionally good prime lens is the pancake styled, EF 40mm f/2.8 STM which has been around for just a few years. It is reasonably sharp wide open (@ f/2.8) and has the same weight as the EF 50mm f/1.8 II - only it's a lot more compact and pocketable. If 50mm is a bit too "tight" (in terms of framing) for you, the 40mm will give you a field-of-view that of a 64mm lens on a full frame. You get to fit more details into the viewfinder but its DoF will not be as thin as the EF 50mm f/1.8 II for the same aperture value and subject distance. You'll also need to move closer to the subject to fill the viewfinder and to get a blurrier looking background.

The catch is that EF 40mm also costs about twice as much and loses one and a thirds of a stop in light transmission due to its f/2.8 maximum aperture.

"Should i upgrade it with 50mm prime lens or any other?

There's no right answer to your question. You can take portraits with 28, 30, 35, 40, 50, 55, 60, 85, 90, 100 or 135mm prime lenses depending on the perspective or the "look" that you want. The only reason why newbies are recommended to buy the EF 50mm f/1.8 II is because it's the lowest priced lens from the Canon EF range.

If you frequently shoot portraits with your kit lens at maximum zoom (55mm) then the EF 50mm f/1.8 will definitely give you sharper images at that focal length compared to your kit zoom. :o)

Not sure why but I have found the 50mm 1.8 to be my favourite lens, I have the 1100d and the 50mm does have some restrictions especially indoors or in a small space as you obviously cant zoom out. Saying that I love playing around with the depth of field and find it produces results that the kit lens just cant do.

One of the sharpest lenses I have and very usable, have used it for Landscape, Portraits and everything in between. Great value for money!

Sanchitgupta100:

50mm will be definitely a great upgrade if you are referring to low light. it allows alot more light (easily 2x more) as compared to your current 18-55 (f3.5-5.6). Which means, you can shoot with lower ISO or shoot in slightly darker conditions.

**Personally, I never find using it at f1.8 to be soft or unusable to my untrained eyes. And I simply love to use it at f1.8 for portraits or for other use (like flora close up).