I found the free one only later after making the purchase of the pay game. The pay game I think is better but it's hard to knock FREE. The Free version works great.
Solitaire Favorites HD is the version I like. Have been playing this persons version since before the app store was available (jail broken iPod touch) to the official touch version and now the iPad version. It has Klondike, Freecell and Spider. Not fancy but has a nice background and and card back graphics. Smooth gameplay. The current version also has statistics which is a nice addition. It is 99 cents.
My favorite is AcidSolitaire, although not all of the graphics are HD. Eric Snider's Solitaire is very nice. Solitaire City has tons of games, but the artwork is ugly, and the interface could use some work.
My most favorite high quality Solitaire game with many variations (35) and priced $1.99 is Solebon. I've played the Palm version since 2003; it was always FREE and for high res screens so I didn't mind paying a small amount for this one. Looks/plays great on iPod Touch, iPhone and also iPad (I use all 3.)