It depends on your situation and needs if you need Secure DNS or another DNS service other than the DNS provided by your ISP.
If the DNS of your ISP is slow that could be a reason to switch to Secure DNS or other DNS service. Secure DNS also will give you warning when you are about to go to a dangerous web site:
Safer - As a leading provider of computer security solutions, Comodo is keenly aware of the dangers that plague the Internet today. SecureDNS helps users keep safe online with its malware domain filtering feature. SecureDNS references a real-time block list (RBL) of harmful websites (i.e. phishing sites, malware sites, spyware sites, excessive advertising sites, etc.) and will warn you whenever you attempt to access a site containing potentially threatening content. Additionally, our ‘name cache invalidation’ solution signals the Comodo Secure DNS recursive servers whenever a DNS record is updated - fundamentally eliminating the concept of a TTL. Directing your requests through highly secure servers can also reduce your exposure to the DNS Cache Poisoning attacks that may affect everybody else using your ISP.