which is the Best Investment DSLR Camera among this?

If you loved it why sell it?!!

The image quality from any of the 4 you list will be no better than your ex T2i

Just buy the one you love the most and then spend some worthwhile money on decent lenses that really will make a difference

Well let me correct you a bit. The T3i competes with Nikon's D5100 and the T4i competes with Nikon's D5200.

The D3100 and D3200 are like your Canon T2i.Just the D3200 has a 24mp sensor and newer technology.

Basically the T4i adds more manual control over the T2i with a better sensor and touch screen.The T4i also has more control for making video. The D5200 adds more manual control over the T2i, an amazing 39 point AF system and a brilliant 24mp senor. It also has built in stereo microphones and more manual control while recording video which are two things the D5100 didn't have.

Just a side note the T2i is still a great camera. What you need to do in the future is invest in lenses not camera bodies. Camera bodies are always going to change and its not smart to keep "upgrading" whenever a new body comes out. Instead buy lenses, they will allow you to do more and also give you better results.

The T3i,T4i,D5100 and D5200 are all about tied so its up to you to decide what you like better and what you find to be the easiest for you. I personally shoot Nikon but that's me. In the end its up to you not us to decide.

In the mean time once you decide on what brand to go with make sure you first learn the craft and then invest in lenses not camera bodies.

Nothing you can buy now is going to be an investment - the tech changes too quickly and old stuff becomes oudated. Not like 50 years ago when you could buy a Leica or Hasselblad good for decades.

The T4i is the best of these by quite a bit in my opinion. I have the 7D which is the 650D (T4i)'s bigger brother and it is stunning.

Video is smooth and has plenty of options. Image quality probably the best non full frame you can get and it is fast and easy to control

DSLR's are expensive and price depreciates quickly in time. They are not good investment items.

If you intend to invest time and effort to learn the craft of photography though then any dSLR will do for that matter. Budget will dictate what you will get. Ideally, get the most expensive you can afford for more satisfaction.

Being a Canon guy I'd recommend either of the Canon cameras.

i have the d3200 and its amazing, the images are crisp and clean, the colors are great and in my opinion nikon's are just easier to understand

Since you shoot so much video, consider the Sony lineup.