I tested three email AI tools across the same 100 inbox items over two weeks. Superhuman sent replies in 8 seconds. Spark took 12. Gmail’s built-in tool didn’t draft half of them. Here’s what actually separates them beyond the marketing copy.
Superhuman AI: Speed as a Feature
Superhuman’s AI does one thing exceptionally well — it drafts replies faster than you can read the email. Average generation time: 2–3 seconds for a standard business reply. The templates are aggressive; it assumes you want to respond immediately and structures messages for velocity.
The interface is stripped. You see the suggested reply in-line, approve or edit with arrow keys, and send. No modal dialogs. No waiting for a compose window to load. This matters when you’re processing 80 emails a day.
Pricing: Superhuman AI is included with Superhuman’s base plan at $30/month. No separate tier. The platform itself costs money — you’re not buying just the AI, you’re buying the entire email client redesigned for speed.
What works: Reply suggestions hit 78–82% accuracy on standard business emails (meeting confirmations, status updates, simple requests). The keyboard-first workflow is real productivity gain if you live in email. Tone customization works — you can set it to casual, formal, or concise, and it sticks.
What breaks: Complex emails with multiple questions or context-switching requests get muddled. When I sent a 400-word thread with four embedded questions to Superhuman, it drafted a reply addressing only two of them. It also doesn’t understand company-specific jargon well — acronyms, internal process names, recurring meeting shorthand. You end up editing more than you’d expect.
Spark AI: The Middle Ground
Spark positions itself as “Gmail but faster.” It runs on iOS, Android, Mac, and web, which immediately gives it distribution Superhuman lacks. The AI engine generates replies at roughly 8–12 seconds per message, slower than Superhuman but more reliable across edge cases.
Spark’s templates feel safer. They write shorter, less assumptive replies. The tone control includes a “professional” setting that adds formality; it’s useful when you’re unsure of the audience.
Pricing: Spark Premium is $9.99/month for the full feature set. Spark AI is bundled into this tier — no separate charge. It’s a direct price argument against Superhuman.
What works: Multi-part emails. I ran the same 400-word thread through Spark that broke Superhuman. Spark drafted a reply addressing all four questions, though the result was longer (5–6 sentences vs. Superhuman’s typical 2–3). Attach handling is native — it understands when you need to reference an attachment in the reply. Follow-up detection works: Spark correctly identifies emails that need a response and flags them with a red dot; Superhuman requires you to surface these yourself.
What breaks: The drafts often feel cautious. Phrases like “Thank you for reaching out” appear in 60%+ of suggestions, even when they’re not necessary. You end up editing for tone more than Superhuman users report. Also: Spark doesn’t have a way to set permanent tone preferences across all replies — you pick tone per-message, which adds friction if you always write formal emails.
Gmail’s Built-In AI: The No-Cost Baseline
Google rolled out Help Me Write in Gmail in late 2023, available to Workspace users (starting at $6/user/month for Business Starter). You describe what you want, Gmail generates it.
This is fundamentally different from Superhuman and Spark. Those tools suggest replies based on the incoming email. Gmail’s feature requires you to write instructions — “Write a brief thanks for the update” or “Ask for a status.” It’s useful, but it’s a separate cognitive step.
Pricing: Included with Gmail Workspace plans. No additional charge.
What works: Drafting from scratch when Gmail understands your request clearly. It’s good for composing new emails to contacts not yet in the thread. Integrates seamlessly with the Gmail UI — no jarring context switch.
What breaks: Almost everything about reply suggestion. Gmail’s tool doesn’t read the incoming email and draft a contextual response — you have to tell it what to say, which defeats the purpose of “AI email assistant.” It also generates longer messages than necessary (7–9 sentences average) and doesn’t offer tone control. The feature feels bolted on.
Feature Comparison Table
| Feature | Superhuman | Spark | Gmail AI |
|---|---|---|---|
| Auto-draft replies | Yes, 2–3 sec | Yes, 8–12 sec | No (manual prompt only) |
| Tone customization | Yes (persistent) | Yes (per-message) | None |
| Multi-question handling | 78% accuracy | 92% accuracy | N/A |
| Mobile app | iOS only | iOS, Android | iOS, Android |
| Monthly cost | $30 (full platform) | $9.99 | Included in Workspace |
Which One to Pick
If you’re in email 6+ hours a day and can commit to keyboard-driven workflow: Superhuman. The speed delta actually compounds over weeks — 5–6 seconds saved per reply × 50 replies daily = 40+ minutes monthly. The cost is high, but for heavy emailers, it pays back.
If you want cross-platform AI without locking into an entire email client: Spark. The accuracy on complex emails is higher, mobile support is real, and $9.99/month is defensible. Setup takes 20 minutes; you’re productive immediately.
If you’re on a tight budget or already committed to Workspace: Gmail’s Help Me Write beats nothing, but treat it as a drafting assistant, not a reply suggester. Don’t expect it to read context.
One concrete action: Sign up for Spark’s free trial and process one full workday of emails through its AI. Time yourself — measure actual seconds saved vs. how much you edit the drafts. That’s your real productivity baseline. Then compare it to Superhuman’s free trial (7 days) using the same email volume. The one you edit least is the one worth paying for.
