Having played both, I would say that TMO and RFB are equally "realistic" within the limitations of the game. That is assuming you play at 100% realism and use the add-on RSRDC campaign mod.
RFB is probably more accurate on various technical aspects, but TMO is more immersive. TMO is also more current since it includes Nisgeis's 3d TDC mod. I have been trying to integrate it into RFB, but it is slow going.
The best way to decide is to try both and see which one you like best.
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