Your website actually seems superfast to me
While I'm a W3 Total Cache fan, it has two drawbacks: it consumes much more memory (a trade-off for improving performance) and it's a pain to configure (every website and theme will require slightly different tweaks). The trick seems to avoid PHP FastCGI and just use the regular PHP: it's slower, but also consumes less memory.
If you don't want to bother with a very complex configuration, WP Super Cache is a safe bet.
Something that will "magically" improve your performance without any costs or risks is just to activate CloudFlare. DH is a CloudFlare partner, which means that all you need to do is to register a CloudFlare account, and then use the DH panel to connect your website to your CloudFlare account. CloudFlare is a caching mechanism in the cloud — your website will actually be delivered out of 14 data centres spread around the world (instead of just from DH's main data centres) and you might expect that half of the traffic will be served by them.
Another nice thing that I'm using on most of my sites is Jetpack. That's a WordPress mega-plugin (with lots of modules) which has been developed by Automattic, the same company that created WordPress. One of the recent features they've added is Photon, which will host all images on your blog posts on their servers (and provide an automatic resizing mechanism for those images — great for tablets and smartphones!). This means that a lot of traffic will be pushed out of DH and be served out of the data centres for WordPress.com. You also get stats, spam control, much nicer comments, and lots of added niceties.
But really, I'd say that your website already loads so fast that there will be few opportunities to improve it I wish I had mine loading at the same speed...