The main thing I'm thinking about is robustness and lack of maintenance. One advantage of RTGs is that you could distribute power wherever it's needed. RTGs are

The main thing I'm thinking about is robustness and lack of maintenance. One advantage of RTGs is that you could distribute power wherever it's needed. RTGs are essentially maintenance free (decades) over the lifetime of the fuel. There are suitcase-sized power plants that NASA have proposed, but I have no idea how feasible they are - or what the maintenance requirements are. I've not been able to find any actual papers on the subject, just the usual gushing science press. Safety seems to be OK, but these are incredibly complicated systems requiring liquid metal cooling (for a start).