what is the best camera now like sony or canon ( what model?) or the mirrorless cameras?

The best camera is the one that despite brand names will have the functions and features that will best work for the type photography you want to do. To determine this you need to understand how you will use the camera and then do your homework to find the best fit for you.

None will last a lifetime, though the lenses might. So consider the body as an expendable thing that needs replacing after about 5 years.

'Best' depends on what you need the camera to do. Cameras other than Sony SLT's (DSLRs without a mirror that flaps up and and instead simply stays in place allowing some of the light to go to sensors) and mirrorless like NEX, will have optical viewfinders using either a pentaprism or penta mirror arrangement. Optical viewfinders are better for action photography as they are less strain on the eye while watching for decisive moments and also don't eat the battery. The ones on entry level DSLRs though are quite small so you ideally need the mid level model of Canon or Nikon (60D, D7100) which have larger brighter finders. Pentax viewfinders are the nicest at entry-level.

For video however the big 2.4MP OLED EVFs on Sony SLT Cameras are easily better, and they help you around manual focusing for stills thanks to Focus Peaking technology from video (it highlights the area of microcontrast or fine focus as it moves through the depth of the image.)

So, look carefully at what's on offer and match it to your needs. Consider that pro-level cameras will be more robust and have a greater number of shutter actuations before they die.

Canon 3t rebel