I'm thinking of buying a domain name for my technology startup. The .com is taken (but unused) and so I want to buy a .io or a .co domain name. What are the pros and cons of each? .co seems to be cheaper on most sites, but .io seems more common.
By the way, I'm thinking of using Namecheap as a registar. Just assume: there isn't any way that I can get the .com and no, I'm not going to do a variation on the name or change it just so I can get the .com.
The cheaper one
Also Namecheap is great. Not a lot of people seem to use it though, so domain transfers may be slightly more annoying if you want to buy/sell domain names from other people.
Nobody mentioned the many hundreds of generic top-level domains (gTLD) that are now available such as .tech .store or .london Whilst you appear to be set on a specific name, if it is a single word (invented or otherwise) one of these new domains will give you a significantly neater and more unique identity, however if it's a longer or two-word name this would effectively make it three words which is not so advantageous nor memorable. .com is of course the best as it is immediately recognisable and doesn't count as an extra word to be remembered.
The problem with the new extensions is most users don't yet know about them and might not realise it's a website if just typed like so you have to make it clear using which starts to look messy again. You can however just make it explicit «visit our website example.travel» or underline it in blue!
I can't say many normal people have any idea what .io or even .co is and so they are far less preferable than the new extensions which at the least explain their associations. If your target audience is not techies or media types, don't use a ccTLD unless you're based in that country where of course everybody knows it. An exception is compound short link domains (e.g. bit.ly) when automatically generated or embedded and thus rarely interacted with (typed or viewed) by a user, but *not* if the user is expected to remember its peculiar structure!
Someone mentioned spam — less a problem based on domain names, but rather the originating server (a VPS or shared is likely to lead to trouble). If you pay for email deliverability through a reputable service or have an established dedicated mail server this is no issue. Spam is of course immediately a problem if you send things the recipient didn't ask for or expect.
.io is more common on tech projects and products but is getting very popular on other genres of companies too. So it's a very nice alternative.
.co is a nice one too and personally I find it more appealing, but at my project (http://disparei.co) I get a lot of mishearing of people not used with the .co domain and it's very common for they to type ".com" instead of .co at their browsers and reaching at a different website.
Hope this thoughts helps.
A lot of mail providers block .co as a lot of SPAM comes from .co domains.
However there are potential politically bad reasons for registering a .io domain as it represents the Indian Ocean Territories where the British Government forcibly expelled the indigenous population from the largest island Diego Garcia to build a US Air Force base.
The islanders have tried to sue the British Government ever since to get their islands back.
Though the domain isn't run by the Gov, it allegedly receives payment for every .io registered.
This has been discussed previously here. The .co domain is -mainly- used for companies/entities located in Colombia, the south american country.
This is less about which one and more about how you create distinction in the marke. What you save in buying the .com (if it were even available) you need to allocate back to clear and concise marketing acumen.
If your company is technical in nature then .io or .ai, ... domains might be perfectly reasonable. If you look at many .io domains, mainly they out of the tech scene. .io works well also if you might keep it, as part of your actual company or product name. Like platform.io. If you are not a tech business I would not use it. Can't really comment on .co, but that says a lot right there, it's not prevalent.
If your startup is selling to other technology companies either .io or .co will do. If you are selling to non tech buyers or consumers, it is very risky. You would spend few minutes in a sales call explaining why is it is .co or .io and not .com.