Having them at the bottom isn't the end of the world. In fact it can be benefitial. I can't find the paper at the moment but here was a study showing that to oxygenate the water and have a good turn-over powerheads should be placed at the bottom to push low-oxygen water to the surface rather than having the pumps try to push high-oxygen water down. After reading that I actually moved one of my powerheads down to the bottom corner and have it pointing forward and up at the front glass. This got rid of a big dead zone in my tank.
I'm partial to the Vortech's for a number of reasons (though I'm still too poor to buy one), so I'm inclined to think it'd be nice to get those over the others you mentioned. Personally, I'd go the easy route and place them on the sides of the tank but there is also the option to put them on the overflow. Make two waterproof boxes out of thin plastic and put the dry side in there. The magnets in the Vortech will hold both the box and dryside in place without issue. I've seen this done with square-sided juice containers that had the tops cut off them. Worked like a charm. If you were closer I'd make you a completely sealed box with a heat sink so that you could put the dryside anywhere and not have it overheat.
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