They’re written to be “smarter” in different ways, so it depends on what you mean by smart.

**Sherlock Holmes (Conan Doyle)**  
- Strengths:  
  - Lightning‑fast observation and deduction (cigarette ash, mud on boots, type of clay on a walking stick, etc.).  
  - Broad, eccentric knowledge base (tobaccos, soils, perfumes, violin, chemistry).  
  - Brilliant at reconstructing physical events from minute clues.  
- Limits:  
  - Much weaker on psychology and emotional nuance; often needs Watson to prompt human reactions.  
  - His brilliance can be brittle: when a clue is missing or misleading, he sometimes stalls or broods.

**Hercule Poirot (Agatha Christie)**  
- Strengths:  
  - Psychological insight: “the little grey cells” are as much about motives, lies, and character as about physical clues.  
  - Works from patterns of human behavior; often solves cases with *fewer* physical clues than Holmes would like.  
  - Very systematic: builds timelines, tests alibis, and runs mental “experiments” on suspects.  
- Limits:  
  - Less interested in physical forensics than Holmes; he often ignores details Holmes would obsess over.  
  - Sometimes relies heavily on confessions or dramatic reveal setups.

**If you force a comparison:**

- **For raw observational/forensic brilliance:** Holmes likely comes out ahead. Put them in a room with a crime scene but no people to question, and Holmes has the advantage.  
- **For psychological and social intelligence:** Poirot is stronger. Put them in a room with suspects but no crime scene left to examine, and Poirot has the edge.  

On “overall” intelligence, authors design each to be nearly infallible *within their own worlds*. Christie sometimes gives Poirot cases (e.g. *Murder on the Orient Express*, *Curtain*, *Five Little Pigs*) that require deeper moral and psychological juggling than most Holmes stories, while Conan Doyle gives Holmes puzzles that heavily reward scientific observation.

So there’s no canon‑correct winner; it’s more accurate to say:  
- Holmes is the superior **forensic/logical technician**,  
- Poirot is the superior **psychological/strategic thinker**.  

Which you count as “smarter” depends on which kind of intelligence you value more.
