I've been using MP3Tag exclusively for years and it's still by far my favorite. I have a couple of minor suggestions regarding the UI for auto-tagger dialogs that I think would make it even better. So there's no confusion, I'm talking about the dialog in the attachment below.
First, the two list boxes in the Tracks frame. It would he helpful if when you select an item from one list box, that item was also selected in the opposite box (both boxes would need their HideSelection property changed to False). It would be a more "certain" confirmation that all tracks on the left line up to the appropriate files on the right. Also when the list boxes scroll vertically, you could scroll both boxes so they are always synchronized with the track alignment. And if the length values are similar (within a few seconds) from left to right, color the length cell text in green, otherwise maybe red for a large discrepancy.
Also, if there is no Cover available, allow drag+drop to insert one, just like it works in the Extended Tags dialog.