Founders ask me this all the time, usually as if one of them is just better. Neither is. They do different jobs, and which one to start with depends on how your customers buy.
I should say up front that Google Ads is my specialism, so bear that in mind. But there are plenty of businesses where I'd tell you to start with Meta, and I'll explain which.
The basic difference
Google Ads catches people who are already looking. Someone needs a plumber, types "emergency plumber near me", and you're there at that moment. The intent is already there before they see your ad.
Meta works the other way round. People on Instagram or Facebook aren't looking for anything. They're scrolling. Your ad has to make them want something they weren't thinking about a minute ago.
Nearly every decision comes back to that.
When I'd start with Google
If people already search for what you sell, Google is usually the most efficient first place to spend. Plumbers, accountants, dentists, a specific product people know by name.
It also suits bigger, more considered decisions. When someone is about to spend real money on a service or fix an annoying problem, they tend to search and compare first.
B2B buyers search a lot too. They look up suppliers, solutions and comparisons. (If you want a social channel for B2B, LinkedIn is usually a better fit than Meta.)
For local businesses, Search and Maps put you in front of people nearby who need you now.
And if you don't have much in the way of photos or video yet, Search ads are text. You can get going without a shoot.
When I'd start with Meta
If nobody is searching for what you sell yet, there's nothing for Google Search to catch. That's often the case with a new kind of product or a brand nobody has heard of.
Meta is also strong for things people buy because they see them and like them: clothes, beauty, homeware, food, fitness. Lower-priced, spur-of-the-moment purchases fit the scroll-and-buy habit well.
You do need a steady supply of good creative, though. Meta rewards fresh images and short videos that make people stop scrolling. If you can keep producing those, it can work very well. If you can't, it gets expensive.
Running both
A lot of businesses end up using both, and they work well together. Meta introduces people to the brand, some of them later search for you on Google, and your Search campaigns pick them up. Google brings in people who are ready to buy, and Meta can remind the ones who left without buying.
One warning if you run both: each platform tends to claim the same sale. Add up the conversions from both and you'll get more than actually happened. Look at your real sales or leads to see the full picture.
Working it out for your business
Start by checking whether people search for what you sell. Google's Keyword Planner will tell you in a few minutes.
Then think about how long your customers take to decide. Minutes and feelings point towards Meta. Days of research point towards Google.
Be realistic about budget. With a small budget, doing one channel properly almost always beats doing two badly.
Be honest about creative too. A Meta account without decent images and video will struggle.
Whatever you pick, set up conversion tracking before you spend anything.
What I usually suggest
If people already search for what you offer, I'd normally start with Google Search, get the tracking and landing page right, and add Meta once you know what a lead or sale costs. If they don't search for it yet, I'd start with Meta to build awareness, then bring Google in as people start searching for you by name.
Either way, the first channel is there to teach you things: what your customers respond to, what they cost to win and what they're worth. That's what makes the second channel work.