1) some say the 15-85mm is much sharper then the 24-105mm.... also i use the 600d and not sure if 24-105mm x 1.6 crop would be really good for an everyday lens....
2) yes i do like the 50mm 1.8 but i am having some serious issues with focus..... it fails to focus correctly many times when the lights are low.... also i dont really see myself using this lens very often in very fast situations...
3) yes i do like the 55-250mm but i dont see myself changing the lens very often because of my usage....
i use the camera for random shots... like friends family etc... it becomes very pain full trying to assemble the flash, adjust the bounce, change the lens , take a pic then review then again retake...
in spontaneous situations it becomes very unpractical like the other day couple of friends went to a cafe for lunch..... half of the time it took me to adjust the bounce, then change the lens... friends would keep moving... and after a while both me and my friends lost interest..... so we kept the camera away and enjoyed our lunch :D....
after seeing this, i am thinking of just keeping one lens......