The 55-250mm is far supreme to the 75-300. It is one of the best IQs you can get without paying a hefty price (They do call it the nifty two fifty). Moreover, you need IS for that long of a focal length which you don't have with the 75-300.
And no, the T3 is not better than the T1i. The T1i has a larger LCD, 4x higher resolution screen, higher ISO, better movie mode, better viewfinder, and a slightly bigger sensor. The list goes on but you can see that the T1i is far supreme.
Anyhow, the Canon kit lens are quite amazing. They are very sharp and decent color especially for its price.
I would definitely grab the T1i over the T3 and the 55-250mm IS over the 75-300