The best way in iMovie is to import from your card directly to iMovie with the original file structure. It will be converted to Apple Intermediate Codec on import.
If you have Final Cut Pro X, import into FCPX from your card, and it will convert to ProRes 422 rather than AIC. ProRes is better if you are applying multiple renders, but this is not an issue for iMovie.
For why your AVCHD files get bigger, see my post here.
Thanks for the great feedback.
I do have struggles though in general, part of which originates from my camera itself.
My camera still has a tendency to record an interlaced effect even though my settings are confidently selected to progressive (I have 50i and 25p to choose from - 25p is my selection).
However, when I use Toast Titanium, I have an option to select the source video to be deinterlaced, but Toast does not do a good job at deinterlacing, compared to Handbrake. The benefit of my Toast Preset is that I can covert the video to an Apple Intermediate Codec, which means that when the files are imported into iMovie, the process is rather quick.
When I convert using Handbrake, the software does a pretty **** good job at deinterlaing, but the downside is that I cannot find a preset that makes import into iMovie satisfactory.
So, in light of all this long discussion I gave, my question is really, what is the best file converter for iMovie to convert MTS files that need to be deinterlaced.
Thanks for any help!