I have used both. When I used Linode, I never experienced a downtime. Ever. On DigitalOcean, I experience many (includes timeouts, and slow response).

For something serious, I recommend Linode. But the cheapest setup is $20/month. For testing, or to spawn many machines, real fast, cheaply, DigitalOcean. Can't beat $5/month or fractions for hourly use!