In short, Digital Ocean is a great VPS company because,
+ They offer SSD VPS at an affordable price
+ Customer service is great
+ Uptime is also great
+ You can create new servers within a minute
+ They also allow hourly billing, which is good for one time experiments where you can launch lots of servers for some period without paying much.
+ $5 per month plan offer 512 MB RAMm 20GB SSD and 1TB bandwidth, enough for side projects or if you're creating your first website or application. You can always upgrade/downgrade if necessary.
+ They're reliable company backed by some reputed ventures/people in the industry.
+ They also offer backups/snapshots (manual backup is free of cost)
+ Dashboard/Admin panel is simple and intutive
+ There are lots of pre-configured templates available (for popular CMS/frameworks) that will save your time when launching new servers
+ Lots of tutorials available to help you out when you're stuck, so even if you're new to server admin stuffs you can easily get things done.