Post a link to one of your vids, I'll view it when I have time and can give you a proper answer.
For now here are a couple of basics for getting a vid without compression or resizing artifacts.
When editing - make sure your project is set to the same size, ratio and FPS as your camera footage.
When exporting - again make sure the output is the same dimensions, FPS and ratio and DON'T export to a compressed format. Export to an uncompressed format like AVI. This will be a pretty huge file but it won't have artifacts.
Use a decent video conversion tool to add compression AFTER export (here you can also resize - but make sure that you resize properly, i.e properly scale the footage don't enter random numbers, if your footage doesn't cleanly scale to the dimensions you want then leave black bars or crop to even it out, don't stretch your footage).
For converters try:
Free - Handbrake, has a "youtube" output setting and its H264 conversion is good.
Cheap - Any Video Converter, again has a "youtube" setting and its H264 output is good.