I own several RB's, 2 1000S's, and several 645 Pro TL's.
That said, with the given choice of RB67 or 1000S, an Rb67 Pro SD is the better choice. Much more versatile, larger native negative with the ability to shoot other formats like 6x4.5 and also 135mm panos with adapters. Plus having separate backs is nice.
I know there are many here on the forum that will extol the virtues of the 1000S and say its far superior to the Pro TL versions, but to me the 1000S is a headache. Ergonomics aren't great with the prism finder, and the WLF has went to crazy price levels in the past two years to where it costs more than a good body. They are prone to frame skipping as they get older and if they haven't had a CLR. And they are heavy for what they are. Don't forget to factor new light seals in for any purchase as most have been run hard and put away wet.
If you add in a 645 Pro TL as a potential choice, and want portability, it may be the front-runner here. Its lighter than the 1000S, has separate backs, and has the same great lens choices as the 1000S. and no light seals - it has light traps. It can be set up super light with a WLF and a hand winder crank, which is what I like to carry on longer hikes. Add a metered prism and a grip, and it functions like a familiar SLR. I know someone will chime in about the mirror stop being an issue when it breaks, but its an easy fix for DIY folks. The other knock is that some will say its plastic, but if one does a little actual research they will see that it has a metal chassis that's covered with plastic, like modern pro-level DSLR's. I have dropped a few and have been fine. For me my only problems with them over the years has been one that stopped working (turned out to be an easy fix with a youtube video's help), and I had a back go bad. To be fair I had an RB67 ProS body wear out and was not fixable, and several RB backs go bad over the years, so its no worse in that regard.
Jeremy