okay there seems to be a lot of wrong concepts here:
1. the KIT lens is crap at auto-focus:
what kit lens are you talking about?? if it's the 18-mm IS canon lens, check out the following pictures, i'm sure most of them are taken using Autofocus, as manual focus using the small focus rings is PITA. i ve used the 18-55 fr 2 years and with decent light and correct af selection it's always spot on.
http://www.flickriver.com/lenses/canon/canonefs1855mmf3556is/
2. coz i've reading quite a lot about the canon 70-300 and everybody says it sucks a lot, primarily due to no IS
again what lens are you talking about? there is a canon 70-300 with IS and there is one 70-300 L lens, which are pretty good.. Any zoom lens is a compromise, and if you want the best quality you have to go for prime lenses. afaik, only the 75-300 lenses do not have is in older versions.
check out some images with the non IS 75-300
http://www.flickriver.com/lenses/canon/canonef75300mmf456iii/
3.
maybe some landscapes, some bird and wildlife shooting
you can do a decent amount of landscaping at 18mm end of the kit lens, but for birding you need a fast lens with at 300+ focal length which will be around 460mm on a crop sensor like 600d/1100d.
4. Expenses:
you will be struck with gear acquisition syndrome at some point of time, read about it here.
http://www.f-stopeight.com/confessi...lenses-made-me-miserable-and-loose-thousands/
5. A bridge camera would suit your requirements:
Sensible, if you have second thoughts after reading point no 4.
6. Decide yourself:
So you can get either of the ones in your list and not go wrong because they are good products, and in the end, the person behind the camera matters most.
check out
http://www.flickriver.com/ to see what kind of shots you can take with your available gear and get inspired.
Good Luck!!