I can't tell if the first one would lose it's siphon or not, but most correctly built overflows don't lose siphon (or else they'd be useless). The second one is built to not lose siphon. You should remember though, you should get an overflow box that is suited for your specific tank. Getting one that's rated for a much higher flow rate than you will be using won't work well, as the flow through the tubes won't be quick enough to stop bubbles from collecting in them, therefore stopping the flow.
And by vacuum line, I mean air hose line that's generally connected to the output of a powerhead (which in turn draws air out of the overflow tubes).