These two get compared constantly and they are not really competitors. One is primarily a place to find contacts; the other is primarily a way to send to them at volume. Working out which half your problem is in settles the question in about a minute.
These two are usually compared as rivals and they solve different halves of outbound. Apollo is best known as a contact database with sequencing attached — it answers who to email. Smartlead is built around sending infrastructure — it answers how to get a thousand emails a day into inboxes without burning your domain.
Teams that end up unhappy usually bought the tool for the half they did not have a problem with. If you cannot name your next 500 buyers, your problem is data. If you have the list and your emails land in spam, your problem is sending. If both are true you are buying two products and should price it that way.
Plenty of teams pull contacts from a data tool, push them into a sending tool, and manage the seam by hand. It works. What it costs is two subscriptions, an export-import step that goes stale, and a suppression list that lives in one system and not the other — and it stays email-only unless you add a third tool for LinkedIn and a fourth for the phone.
Both stop at sent. Neither answers the reply, neither books the meeting, and neither notices that the prospect who replied on Friday is still waiting on Tuesday. For a small company where the founder is selling, that gap is where most pipeline is actually lost — not in the data and not in the deliverability.