yeah same here, the blurry and artifact/compressed quality of image and awful lag fps are unbearable (of course there are people who like that, to each their own). NTRview on Wii U is just an average POC. For better and really playable/enjoyable/free stream without a capture card, cuteNTR for Raspberry Pi or Kit Kat for Windows are the best options.
At least some of this doesn't make any sense. When you connect to the 3DS from any NTR streaming client, the client sends a few flags including one for the JPEG image quality, and then the 3DS generates the images to those specifications. You can't get better images by using a different client because the streaming
server is creating those. If you're getting more artifacted images in one client than another, it's only because that's what you're telling the 3DS server to send. i.e. If you want better images, configure your settings to request them.
Likewise, the Wii U client doesn't inherently have "awful FPS", you apparently just have awful connectivity on your Wii U. The framerate you'll get in any NTR streaming client is entirely down to the network connection quality between your 3DS, your router, and the client (whether that client is a PC, Raspberry Pi or Wii U). The Wii U's wifi radio isn't the greatest, which is why Nintendo sold a USB ethernet adapter which many people prefer due to the difficulty in getting a decent connection via wifi. If your PC and/or Raspberry Pi have more stable network connections, you'll have a better time using streaming clients on those, but that's got nothing to do with the clients themselves.
The only major exception to the rule of "clients don't matter, network stability does" is how they handle missed/incomplete packets. This is one case where the Wii U client can legitimately be argued to be worse than others, because it trades some latency reduction for poor handling of bad packets, which can result in flickering/corrupted frames instead of dropping those frames as other clients do. If your network is stable, this isn't often a problem, but if your Wii U is missing a lot of packets you'll have a better time on a different platform where a) packet loss is handled better or b) packet loss doesn't happen as often due to a smoother network connection.