Although my post is too late, I hope it could be useful to you.
If you would like to edit the mts footages with iMovie, I suggest you convert mts videos to Apple InterMediate Codec (AIC) MOV. If you would like to edit the mts videos with FCP, I suggest you convert mts to Apple ProRes MOV.
After transferring the mts footages from you camcorders, neither iMovie nor FCE will recognize the videos automatically.
What I suggest you do is to transcode MTS videos to Apple InterMediate Codec (AIC) MOV or Apple ProRes.
What I am using is this smart MTS Converter Mac program: Brorsoft MTS/M2TS Converter for Mac. It's able to convert/transcode AVCHD/ AVCHD Lite footages (*.mts, *.m2ts) to Apple ProRes, Apple InterMediate Codec, Avid DNXHD compatible with FCP, FCE, iMovie and AVID.
The best important factor appropriates me to choose it is its large variety of video formats. I feel it is very dependable and does exactly what I need it to do. Overall I am very happy with it and feel it was a good investment of my money.
So I think it's worth to try and you can have a free trial at first.
For more information please refer to: http://www.brorsoft.com/mts-converter-mac/index.html
Here is a tip which may be helpful to you:
Pay attention to and always check your MTS file frame rates. Footage shot at 60p will have the best quality when converted at 60fps, although you can reduce the file size substantially if you convert at 30p. If your video footage was shot at 60i, it's best to select 30fps or 29.97fps as the preferred frame rate.