Is there a reason Harry wouldn't get Suffolk? I hate Sussex. Too many bad puns can be made there.
Main reason against it would be there is already an Earl of Suffolk. The current earl is the 21st earl. Oddly his second wife and mother of his heir is the stepmother of Serena Standhope, the countess of Snowden (Anita after her divorce from the earl, was the second wife of Serena's father). The current creation are descendents from Anne Boeylyn's mother's family, the Howards.
It is unlikely to be both an earl and duke. Except when they are held by the same person (as when an earl was elevated to duke).
Suffolk also isn't a historically royal title, which doesn't rule it out. Though most titles have some bad history, Suffolk....
- The Last duke of Suffolk was Henry Grey the father of Jane of the nine days. He was created duke after the death of his wife's younger brother. Of course like his daughter and her husband, he was executed for treason.
-Charles Brandon was his father in law. He of course married Henry VIIIs sister Mary. Likely his close childhood friendship with Henry was the only thing that saved him from execution marrying her without permission. His sons all died young.
- before them we had the De la pole family. The second duke was married to the sister of Edward IV and Richard III. The first and third dukes were both stripped of their title due to treason charges. The first was banished but he was captured at sea and beheaded. The third was executed by Henry VIII. The heir of the second duke was at a time heir to Richard II. The third dukes younger brother claimed the earl title, and had French support to the British throne. But he died in battle with the French army, before a planned invasion of England (with the support of both the Scots and French)
I don't think we can rule out titles due to bad history. Because all titles have bad history of some kind. But Suffolk seems pretty highly unlikely
1. earl of Suffolk
2. no royal history (never been granted to a royal prince)