Softlayer's network is crap compared to google and aws. That being said in my previous company we used a combination of Softlayer (for dedicated machines) and AWS for cloud. There is definitely a use case for each, but as Nrsolis mentions there is additional cost in things beyond the cost of the initial hardware itself.
At least with AWS you get placement groups, which can help a lot. With Softlayer we saw entirely too much packet loss on a regular basis, and they try to upsell you on things to "fix" it.
