The pragmatic answer
If your org already pays for Microsoft 365, Teams is free — use it. If your org is a startup, growth-stage company, or in the tech/creative industries, you'll almost certainly land on Slack regardless of what the CTO says.
Where Slack wins
Integration ecosystem
Slack has more native integrations with developer tools, design tools, and modern SaaS. If you live in GitHub, Linear, Figma, Notion, PagerDuty, Datadog — Slack will feel like home.
Speed and UX
Slack feels faster. Keyboard shortcuts are deeper, search is more accurate, and the desktop client uses less RAM (a real thing engineers care about).
Culture
Slack's emoji reactions, custom emoji, threading patterns, and channel naming conventions have become the lingua franca of startup work culture. New hires onboard faster because they already know how it works.
Where Teams wins
Cost (if you already pay for M365)
Teams is bundled into M365 Business Basic ($6/user/month) and up. Slack at the Pro tier costs $7.25/user/month on top of whatever email and office software you're already paying for. For a 100-person company, that's a real number.
Native video & calling
Teams meeting infrastructure is more mature than Slack's Huddles. PSTN calling (real phone number routing through Teams) is included in higher M365 tiers, which Slack doesn't really compete with.
Enterprise compliance
If your company has serious compliance requirements — data residency, e-discovery, advanced audit logs — Teams under Microsoft Purview is hard to beat. Slack Enterprise Grid is good, but Microsoft has a stronger story in regulated industries.
Price comparison
- Slack Free: limited history, fine for <10 people
- Slack Pro: $7.25/user/month (full search, unlimited integrations)
- Teams in M365 Business Basic: $6/user/month (includes email, calendar, basic Office apps)
- Teams Essentials (standalone): $4/user/month
What to actually do
Don't try to migrate. Whatever you're on right now, stay on. The cost of switching team chat platforms is enormous in lost institutional knowledge (search across years of decisions) and culture friction (people complain about it for months). The only valid reasons to switch are: cost has become a real budget item, or compliance requires it.