HN has a large, established community. It's ranked 1,644 worldwide on Alexa, even higher than Product Hunt which is ranked at 3,563. A successful showing there can bring with it a large following.
There are no arbitrary hoops to jump through on HN. Everyone is free to post there as long as you follow the guidelines. The submission are judged simply by the users via votes.
BetaPage appears to be pretty early on and won't currently drive the sort of traffic that Product Hunt does or have the same sense of community. It's currently ranked 144,269 on Alexa which indicates that it won't bring you much traffic to your product.
While in Jan of 2009 it had 600,000 unique monthly visitors and Alexa put it at #8,599 website worldwide, it has since lost close to all of its traffic and ranks at #140,707 worldwide.
SimileTo makes it easy to quickly find stuff. The lists are organized by likes which floats the best content to the top, and helpful tags warn you of undesirable attributes (such as the product being discontinued or if it includes bundleware).