You need to match up the bitrate, or choose a higher one.
Re-encoding video to these formats always loses some quality, but a higher bitrate can better reproduce the original video footage.
When I check my video footage, it's 30mbit. The default profiles in AVS are somewhere around 1.5 to 9mbit. You'll have to tweak them to get the same quality as your source footage. You should also make sure that you're not downsizing your video, for example from 1080p to just 720p.
1080p looks reasonable at anything over 20mbit, but you'll want more if you want to preserve as much detail as possible.
-Kramy