I use Sandisk cards in my cameras, which have never failed. I don't have an opinion on other brands, because I've only used Sandisk.
Why do you want to replace your cards? Your image cannot degrade due to older cards. They store information digitally, so the information either is there or it is not. Cards can fail, but a working card will not cause images to degrade as the card ages.
When I bought my D50 in 2005 and my D300 in 2007, I bought new cards to use in them, and I am still using the exact same cards with no problems.
If you want more cards, or faster cards, or higher capacity cards, those are all reasons to buy more. If your current cards are working and doing what you need (big enough, fast enough), your images will not look any different if you replace them.