Very interesting replies. It seems like the issue with all these answers is that they're all biased (including mine below). Unless you can find someone that has an almost identical portfolio as yours to share their numbers, you're not going to get a conclusive answer.
For example, some portfolios may lean heavily towards made-up words in which case they won't see much search traffic across registrars/marketplaces. Others may rely on popular keywords and trends in which case they'll see a ton of search traffic. Every seller's portfolio is based on their own unique strategy so it's hard to compare numbers.
Additionally, every marketplace has a different marketing budget and the budget isn't always consistent over time which makes it even harder to predict the numbers.
All that said, I'm sure everyone here would agree on one thing. That more exposure is always better regardless of
how much it is (i.e. you never know if that one dude or dudette on marketplace X ends up falling in love with your domain even though that marketplace only brought in 1% of the overall traffic). So more eyeballs are always better.
Now onto some useful data... Alter now has close to 4,000 brandable listings that all point to our nameservers (bias = brandable, although
our inventory is pretty diverse). Since last month we've also been automatically listing our inventory with
our partners.
Here's what our traffic breakdown looks like across the board for last month:
Marketplace: Visitors learned about the domains from our marketplace.
Partners: Visitors learned about the domains via our partners (estimated).
Direct: Visitors learned about the domains by typing them in their browser.
Again, every seller's numbers will vary based on their own unique portfolio (if you're using Alter, you can see your personalized breakdown on your dashboard).