I've replaced my horizontally-polarized 6M loop with a vertically-polarized 6M ground plane and my signal into the repeaters is MUCH better now. I got the SWR down below 2 in range where our local 6M repeaters are (52.700 and 53.010 outputs) and don't even need the tuner. Noise is only S3 where before it was so high I couldn't squelch it.
I used the Arrow Antenna GP52. Great antenna for the price. I'd like to get it higher in the air but for right now the best I can do is about 21 feet and the radials are scraping the shingles. When it gets warmer I'll have the boy get up there and add an extension on the pole to get it up another three or four feet.
One caveat about this antenna: It's a lot bigger than you think it is.