Well, best-seller probably ain't the proper word, but it is nowadays the easiest to find ELCASET recorder, along the upper EL-7.
Released in two versions besides the regular normal simple EL-5 :
• an extra-rare black-face Mediatech M950 for audio/image sync purposes,
• an FM version with a pair of FM calibration pots added.
The latter sees its RM-30 remote plug displaced where the multi-voltage selector is and the vanishing of the DIN i/o.
All versions have FET-charged inputs and variable output (back pot) and a sound which very few cassette recorders can equal : tape-speed is of the essence.
The EL-5 only is the single-motor / 2-head version but one really has to see the EL decks in the flesh to grasp the size of them and their build-quality.
If Sony was asked to OEM its EL decks by Hitachi (Lo-D 9000) and decided to make a Wega ELCASET, both outfits went for the EL-7 and not the EL-5 : high-end is luxury is high-end.
As a side-note, I will allow myself to add that Sony's EL transport control panel still is the most beautiful transport control panel ever.