On price, Rocket.net starts lower at $30/mo against $50/mo for Rackspace. Rocket.net carries the higher rating overall, at 4.9/5, and Rackspace reports the better tracked uptime at 99.99%. Rackspace has been operating longer, since 1998.
If entry price is what decides it, start with Rocket.net. If rating and reliability matter more than the sticker price, Rocket.net has the edge. Either way, read the full profile before you buy — the trade-offs section on each page covers what the summary numbers leave out.