Only real difference is visual preference and hit to the wallet. As mentioned plate bumpers are time consuming, it take me about 8-10hours to make one(cutting it out by hand), which is why most go with tube, either when fabricating their own or buying one. Goldenstatemotorsports.com/(Sac.) is about the best price for a plate bumper, not sure how they can do it for $600, I would charge more, and I don't have shop overhead to pay for, same for their rock sliders.
This hobby necessitates the need for you to either have deep pockets or the ability to fabricate/repair things yourself. If your pockets aren't deep, you should consider talking a welding class at Sierra College(if one is offered at the GV campus), you should be able to build a bumper and sliders as a class project. Looking at their website, it looks like they have an Expo coming up in April, and looks like they have a mobile welding training class http://www.sierracollege.edu/about-us/public-relations/press-releases/2013/04/weld.php
, something you might want to look into. Welding is one of those skills that you pays for itself many times over, I have easily paid for my start up costs(about $600) just fixing/repairing exhausts and non vehicle related repairs/fabrication.