Bad Aspect Ratio in Quicktime on Video from Camcorder
You can use ClipWrap ($50) to rewrap your AVCHD videos to a Quicktime/Final Cut compatible format.

Then, deinterlace your videos using JES Deinterlacer and export them preserving full quality (huge files though).

So the workflow is the following:


Add videos to ClipWrap, select as output the "Rewrap (don't alter video samples)" option and save them to a new location.
Open JES Deinterlacer and drop all videos to input's "hot-box"
Select Project properties:


For 1080p30 go to Project > Deinterlace > Top Field, Adaptive, Local
For 720p60 go to Project > Standards conversion > 1280x720 60p

Finally, go to Output > Export > QuickTime Movie


Settings > Compression Type > Apple ProRes 422 (LT)
and export the video!



So, your videos will be ready to import them to Final Cut.

I hope that helped!

Edit:

If you want to transcode the video files, just for viewing them in Quicktime, then you would have to select H.264 when exporting from JES Deinterlacer, than the Apple ProRes which is suitable for editing.