With this comparison photo, you can see that the Sonic's spikes are kind of wilty or strange, as compared to the Shadow. They're above 'felt strip' level, but they're not as great as possible.

All the plushes here are from the Sonic X UFO Catcher set. Meaning, they can all be won out of claw machines in Japan. Usually plushes found in there aren't the best quality, but here you can see this isn't the case. Rouge has heels to her shoes, her 'hairs' in back, and detailed eyes. Eggman has 3D goggles, shiny glasses, and a felt mustache.

Everyone has fingers, and Shadow's shoes are fully detailed. The eyes are embroidered on, though Rouge's eyes are not the right color, if you look closely. Sonic and Shadow are a bit fat, but still, the likeness are pretty nice and detailed.

These are all by Sonic Project 2004. Bokkun is on this set too, but you need Plushes 3 to see him. Over all, this is a fine set of Sonic X plushes, especially considering you could win them. 

Here's a better look at the X plush set's Eggman. He looks fine from the back, they kept the detail of his coat & the 'fins' at the bottom are floppy as they should be. The detail shot at right shows his cuff, both sides of the cloth tag (so you can see authenticity) his shoe color decals & the details for his face. The goggles are 3D with little colored dots for the 'glass' his eyebrow ridge is sewn on & the mustache is flat felt. This is a good & detailed plush.