It's a tough call as they're very different beasts. The RTS is a vastly superior camera to the 139Q which was a model brought in to compete head-on with the Olympus OM1 and aimed at the well-heeled amateur. The RTS was always aimed at the professional camera and you only have to hold the two to feel the difference - the RTS was designed to take a lot of punishment; I still use my one bought in 1977 with a 5fps PMD drive; all I've had to do is change the leathers once and every 6 years, change the mirror damping foam and light baffles. BUT once you have an electronic problem with the RTS, it is in effect a write-off - your only solution is to buy another or if you know a good technician, buy a damaged one (where the problem is very different) for a few pence and use it as a donor for your own camera. The benefit of the 139Q, apart from slightly more contemporary components, is that they are very cheap to buy in top condition and so can easily be replaced. The RTS is more versatile - winders & motors, Polaroid and bulk backs, even a Scientific version that as a few advantages over the standard model - but is a lot heavier than the 139Q. Both cameras are totally battery dependent (though with a drive the RTS can be powered by AA batteries - not possible for the 139Q). While I would never use a 139Q if I have a working RTS, it would be the cheaper option. Personally, if I was to consider an early Contax other than the RTS/RTSII, I'd go for the beautiful 137MA (not the Auto only MD) which shares many of the features of the 139Q but has the advantage of an in-built motor drive and uses 4 AA batteries and not LR44 cells.