These days, it seems pretty easy to bypass some anti-DDoS services. From my experience, Imperva is one of the best options if you're willing to invest in solid protection. Fastly is also decent, and DDoS-Guard has its merits. However, I’ve found that companies like Cloudflare and Sucuri can be easier to bypass.
I've tested some big websites using Cloudflare and Sucuri, and even with millions of active users and strong servers, I was still able to take them down. On the other hand, Imperva is a different story—it's tough to bring down a site protected by them, and I know some people who sell DDoS services charge over $5,000 just for targeting Imperva-protected sites.
If you're not looking to spend a lot, Cloudflare might be a more budget-friendly option, but just keep in mind that it has its vulnerabilities too.