I've been using 1.9.8 (not a portable version) on a Tails USB key. You can funnel it through Tor nodes, but it requires for some kind souls to keep an Electrum server up on a Tor node. Unfortunately the .onion/Electrum servers seem to be infrequent.

If you use the -1 switch, it keeps it from trying other servers.

I consider this to be very secure. You could be on the most infected computer in the world, and it can't touch this. A hardware keylogger would be the only possible way to lose your passwords, and Tails has several virtual keyboards or Keepass that will defeat that.