Help a new guy w/ lens selection

[blktre]

Hi, new here. This seems like a great forum! Anyways im a beginner just learning my camera and photography in general. Im looking to get another lens. Budget is always a concern. Just about a year ago i bought the Canon EOS Rebel Ti (film) w/ a 28-90mm Quantaray. Ive used the camera few times and enjoy it. I like taking the camera on hikes and shooting nature landscapes, sporting, and just general stuff. So,

I thought the Sigma 28-300 AF would be a nice choice for me. But, i havent gotten good feedback on this lens concerning image/optic quality above 200mm. I will never be a huge photo guru but would like to take some decent pics. Would the 70-300mm lens be a better choice for me? Im thinking the hastle of switching lenses would be worth gaining better optics at the longer focal points. Easing the budget as well........help guide me on which lens i should buy........thanks in advance for all the input! This newbie appreciates it.......Oh, whats APO stand for such as 70-300mm f4-5.6 APO Macro Super II?........Cheers.....