I would suggest using your ElGato.
Record the video in MP4 or h.264. They should be roughly equivalent quality since h.264 is more efficient.
These will import and edit directly in iMovie.
Normally I recommend that you convert mp4 video in HD sizes to Apple Intermediate Codec before editing, but this is standard definition video so it may edit just fine as is.
If you want to convert to Apple Intermediate Codec, there are two ways. (Three ways if you have the EyeTV 3 software).
1) Convert it using the EyeTV 3 export menu.
2) Import to iMovie and choose Optimize - Full
3) Drag the MP4 into MPEG Streamclip (which is a free app) and use FILE/EXPORT TO QUICKTIME. Choose Apple Intermediate Codec for the compression. Then add to iMovie using FILE/IMPORT MOVIE.
The alternative are the Firewire-based DACs from Grass Valley. They will convert to DV, and in my experience do not produce enough qualtity difference to justify spending several humdred dollars more. After all, the original VHS is roughly 400x300 pixels, so it is never going to look like DV from a DV camera.
Personally I use the EyeTV Hybrid with the EyeTV 3 software. I do not know for sure, but I assume the EyeTV Video Capture is very similar, but without the TV Tuner.