Curious about what Slingbox you are using and how you have it connected, and to what?
I have owned the Sling Solo and now the HD Pro, both produced "HD" looking feeds on my iPhone 3GS and now iPhone 4. On my local network over wifi had a very good/HD picture via the web player on an iMac and although the iPad is pixel doubling the signal it's still a decent picture but I assume that will improve nicely if they ever release a iPad specific app.
I have only tried out the Eye TV box/software for about 2 weeks and while it had a decent picture I just wasn't interested in using their UI and interface vs Slingplayer using my cablebox's menu's etc..
As to your last questions, is there an iPad version... not yet but Sling claimed back in March to be "working on one". They have been pretty slow to market with new players in the few years I have followed their apps.