For space travel, escape velocity and cost to leave the atmosphere are the main factors.

I've seen estimates for earth-like planets but wonder if venus and mars are earth-like by their count. Mars might have had a more hospitable past but was it long enough to get anywhere near the time scales we had to develop intelligent life and space travel? Was it closer to asteroid belts? Does Venus provide conditions for complex molecules?

A dense atmosphere sure helps to protect the surface but it also holds back rockets on their way out. But then again, dense atmospheres might not be a problem if lighter-than-air platform launches work: nostr:nevent1qvzqqqqqqypzq3huhccxt6h34eupz3jeynjgjgek8lel2f4adaea0svyk94a3njdqqstjpnthcg63v35v2gx5ls80m3nl4yc0yn5ufr63zkphta4d9yhhmguf0rcn