'Best' depends on the business. Office 365 would give you everything you need. The $5 plan for small business would be good.
You get hosted exchange, 25gb skydrive and domain hosting and a sharepoint site.
By going Exchange you have have all the contacts and calendars that is expected of exchange.
For details about the latest Mac operating system, check out the best business features of macOS High Sierra. Cons of Macs Expensive: All Mac products are expensive.
$60/year per user so for 20 users that is only $1200 per year. You really can't beat that for the feature set and zero maintenance and backup worries
Best Mac For Small Business
Edit: Sync bookmarks would be a per browser thing unless you look into a 3rd party solution like a browser plugin.
Mac Computers For Business
Edit 2: Google Apps for Business is also $5 per month but they give you a deal and drop 2 months when you pay yearly. only $50 per user so still $1000 per year.