You are basically 100% safe if you start with 20x buyin. I would say that you're 90% safe if you start with 10x your buyin and you are a good player.

If I personally had $80 in front of me, I would actually start at the $10s because I know that my ROI there is well over 40%, so my risk of ruin is very low. If you don't know much about your ROI but are confident that you can be a winning player long run, I would say that the $5.50 tables should be OK. I would only play the $3 tables if I didn't really know whether I could beat online SNGs.

Play the $3 to start out, and if you cash in a few of them, go ahead and dabble in the $5 ones while keeping $3 as your home until you feel good about moving up permanently.

As stated, the answer to your question is all in the juice. I would certainly recommend playing $3+.30 or $5+.50 if your site offers them. But I tell people not to touch Party Poker's $5+$1.

I started off playing on the $1 sng's on Ultimatebet. They are a great place to learn and to gain some confidence in your abilities. I found that progessing to the $5 sng's on Pokerstars Party and Full Tilt was a natural progression and the difference in play is almost nil. I don't like the vig at Party so prefered to play on PS and Full Tilt.