[Trav-man]

I currently have the Rebel XT with the 18-55 kits lens. I like shooting landscapes and architecture, which is very difficult to shoot. Shots are indoors and outdoors and it requires a wide end lens and a close-up of details (sometimes one shot right after the other). Now that you know my position, my post has 2 questions in within it:

1. Do you think it would be easier to shoot with both the 18-55 kits lens and a 70-300 macro lens (either the Sigma or the Tamron) or with one lens (18-200 and again the Sigma or the Tamron) I don't know how much of a hassle it is changing lenses when shooting and I am a very novice photographer and only have ~$300 to spend.

2. Out of each one of these lens groups, with lens is the best for the money?

Sigma 18-200mm f/3.5-6.3 DC vs. Tamron 18-200mm f/3.5-6.3 XR Di II Macro vs. Tamron 28-300mm f3.5-6.3 XR Di LD Aspherical Macro

Sigma 70-300mm f/4-5.6 DG APO Macro vs. Tamron AF70-300mm F/4-5.6 Di LD Macro

I have also read somewhere that the Canon Rebel can't use its AF at the 6.3 end, is this true?

Any help would be appreciated. Thanks to Saralonde for her help to this point and informing me enough so I don't sound extremely inexperienced.