We have been using siteground for some time now and we were overall happy with their services, even though there has been some bad times as well. But the good part was they were ready to do things to change the bad to good.
Few of the good things we have noticed over the years is that:
Their support is availabel round the clock and we could talk to someone, but sometimes with some small wait.
They will try to help you and work on your requests fast.
Their high end plans like GoGeek and cloud services are very good in quality.
The GoGeek plan also claims to have PCI compliance.
Their higher support teams have knowledge and even goes out of normal policies to make you satisfied.
Few of the things that they can improve are:
Their first level support is not extremely knowledgeable and has given few wrong informations few times.
For instance, they confirmed once that we will get domain renewal on transfer in and later whenwe did not get, they said according to the policies they give only for new domains.
But when I shared the chat transcript they gaver me a credit to buy/renew a domain.
Their regular prices are high compared to most competetors.
For the same price you will get better offers elsewhere.
For instance, you will get a decent VPS for their GoGeek shared hosting plan. But the first year price with offer is ok.
Quality of starter plans are not as good as other hosting provider packages in the same price.
Though there were no ugly experiences.
However, these are things which they could have avoided:
Though the first level support is very helpful, sometimes their ignorrance irritates you.
Recently we asked for a help, they helped immediately, but some of the functionalities of the site were broken. When we told them about it, they asked us to raise another ticket to their higher technical team. Since they made the mistake, they should have raised the ticket themselves or forwarded the current request to higher level teams. Also, the person and the escalation manager strongly confirmed that something is not possible, but we could do a simple google search and fix it through a change in the .htaccess file.
These things could have been avoided, by confirming only things you know and leaving the rest to people who can answer them.
Our overall experience is still good and I am still a customer of Siteground.