Tech Index. The big one.
Ok, for Werekoala's benefit:
There are four levels of tech (that are sufficiently advanced to get the Vaylen to infiltrate instead of just marching in with ray pistols and telling the fire-discovering inhabitants to report for hulling).
Sub-Index
Zero Index
Low Index
HIgh Index
Sub-Index worlds are worlds that are about as technologically advanced as 20th century Earth. You've got radio, telephones, jets, television, and the like. There specifically _isn't_ a space presence of any sort. From the way folks are talking, I'm guessing we're not going to go with it.
Zero Index worlds about as advanced as 21st century Earth, maybe a little bit more. Computers, internet, nuclear power and weapons are all available. The space presence is limited - ISS-style stations or moonbases, with chemical thrust still the main method of getting around. This can also be used to represent worlds that are dependent on other worlds or systems - the inhabitants can't manufacture advanced spacecraft or other technologies, but can be familiar with them. A Zero Tech Index makes it hard to be a space-faring sort though.
Low Index worlds are the default tech setting. The technologies available include: anti-gravity, fusion power, advanced spacecraft, superconductors, distortion drives (the FTL of the setting), powered battle armour, psychic powers, nanotechnology and AI, cloning and genetic engineering. Spacefarers are A-OK. Generally, low index worlds have system-wide economies, using asteroids, other planets and space stations as necessary. They also can carry on trade, warfare and cultural exchange with other systems.
High Index worlds are the most technologically advanced worlds in Burning Empires. The technologies available include force fields, "transhuman biomodification", the ansible, matter converters, "mini-blackhole reactors" and technology that can fiddle with psychic powers. Basically, a high index world is as technologically advanced as you can get without becoming a post-scarcity economy.
My vote is low index. High Index would be cool, but I don't think it'd fit with the grim and gritty industrial dystopia. Zero Index would shut down the pirate lord ideas, and make the space stations much less independent. Low Index seems like a good balance of sci-fi powers and limitations for the colour we've set up so far.