I have had good success with syndication, but that is because the site editors hand pick posts. My sites gets syndicated by a few large media outlets. The only reason I allowed this was because they put in the canonical tag in the HTML. This shows Google that I'm the content owner and it appeared on my site and to give my site full credit for the work. The syndication gets me large amounts of viewers, so I like that.
Guest posting is also good, but you have to do it in strategic places. Guest posting might not get you good traffic boosts, but it can give you good links back to your site, which is important.
You should consider both.
Rockstarfinance is owned by J.Money of Budgetsaresexy.com. He is awesome, but I don't really consider that site a syndication. He isn't taking anyone's content and putting it on the site. He is actually pushing his visitors to your site if/when you get featured. You can get good traffic from Rockstar.