Most definitely that's a question that needs to be asked, but before you ask that, you need to ask what engines have performance specs worthy of further conside

Most definitely that's a question that needs to be asked, but before you ask that, you need to ask what engines have performance specs worthy of further consideration. If you did it in reverse order, you're liable to get finalists like whatever they put in those volvos with a couple hundred thousand miles on them. :P It doesn't matter how reliable the engine is if it's not performant enough for the envisioned task. As to your question about reliability and track record, it's kinda hard to base the decision on past launch performance since most rockets-engines are built to a specific rocket and vice versa. These things aren't like a used car where you can look at thousands of unique datapoints, or use the same engine in the silverado that you use in the corvette (yeah, this is actually true. different ecu settings, though). And it generally cost prohibitive to do a full dry-run with only a cargo full of, say, bricks, because a single launch costs well north of a hundred million dollars. Instead you have to run a lot of ground based tests and figure a bunch of probabilities. These guys won a one point something billion dollar contract from NASA to deliver shit to the ISS. NASA's not exactly well funded and not exactly known for flying by the seat of their pants, even by government agency standards. In order to win that contract they needed to prove to NASA's satisfaction that there was a high probability that their rocket would get to ISS without a major problem, let alone one as catastrophic and uncorrectable as exploding a few hundred feet above the pad.