full frame is my main concern here. I had been using my friend's Rebel kiss since months and it breaks my heart everytime i return home with cropped images due to the crop sensor.
If the above is your experience / thinking, there are (at least) 2 (possible) issues here:
1) your friend's Rebel Kiss (300D), the first of that 'line' of Canon's 'entry level' DSLRs has been used with the 'wrong' lens - eg using a 28mm lens on a crop sensor (1.6x / APS-C) for 'wide angle' won't really be 'wide'. You need a lens at 17mm to be equivalent of 28mm in Full Frame (FF) format. Don't use wrong lenses (ie expecting the same mm as in FF) for the APS-C / crop sensors (btw, new crop bodies like 700D and 60D are MANY steps better in just about every regard).
2) you don't understand photography - that is, that you think the lens 'won't crop' an image in the first place. What you see through the optical view finder (OVF) in a DSLR is what you get. So, therefore get a lens that you need. Eg, I have the Canon EF-S 15-85mm IS USM, which is a great lens for a APS-C, and very comparable in focal length (and other aspects) to the EF 24-105mm L IS USM on a FF. So get the lens or lenses you need, whether prime or zoom, whether fast or slow.
Generally for landscapes and low light, FF is superior. If you do a lot of low light, maybe the 24-105mm will serve you well, because although it is 'only' f/4 (not particularly fast) - it has IS which will help you in getting steadier hand-held shots than even non-stabilised f/2.8 lenses.
I love using primes (eg f/1.2 ti f/2) for low-light / subject isolation. Zooms for good light, and travel / convenience. Even on a crop, such prime lenses can produce stunning images with shallow depth of field (DOF) and zooms - particularly EF-S like the 15-85mm or Canon's 17-55mm f/2.8 can be really handy and have high Image Quality (IQ).