.com

Google, and probably other search engines too, uses ccTLDs as a "strong signal" that a site is intended for a specific country. Using .at, therefore, wouldn't be ideal for what you describe.

So if your target is global avoid .at, but you needn't use .com - any gTLD should do the trick, and probably be cheaper.

Sources:

http://support.google.com/webmasters/bin/answer.py?hl=en&answer=182192, especially:

ccTLDs […] are tied to a specific country (for example .de for Germany, .cn for China), and therefore are a strong signal to both users and search engines that your site is explicitly intended for a certain country. […] We also treat some vanity ccTLDs (such as .tv, .me, etc.) as gTLDs, as we've found that users and webmasters frequently see these as being more generic than country-targeted"

Edited for relevance, bold emphasis mine.

There are various types of TLDs which are assigned by IANA, time-to-time to organizations (or to countries).

Some of the TLDs are -

- gTLDs -- Generic Top Level Domain; like .com, .edu, .org, .net and various others
- ccTLDs -- Country-code Top Level Domain; reserved by IANA for the countries and are managed by the country NIC (or NIXI or others).

.tv is one of very famous ccTLD assigned to Tuvalu, a small island in Pacific Ocean. Through name, it look like that this domain is related to Television but its not the case. It is a ccTLD.
.ly is also one of very famous ccTLD.

Similarly, .uk is the ccTLD assigned to UK by ICANN.

Its generally depends on government to government policies, as which top level domain they will use for their country specific purposes. And also it also depends which TLD is famous in their region and this generally influence the selection criteria of the residents of that while going for procuring a domain for their own usage.

It may be case that, .co.uk is more famous (or more preferred) in UK; In my region .com is the most preferred one and majority of sites of my region are hosted on .com TLD.

Look at that list for example:

https://en.wikipedia.org/wiki/List_of_Google_domains

This list contains domains used by Google in various regions. It doesn't mean that UK has .co.uk cc TLD. It's just a google choice that they are using google.co.uk in UK region instead of google.uk.

If you query for google.uk; it will show that google also own this domain also.

Kansals-MacBook:~ Kansal$ dig google.uk
; <<>> DiG 9.8.3-P1 <<>> google.uk
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 51848
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;google.uk.         IN  A

;; AUTHORITY SECTION:
google.uk.      122 IN  SOA ns1.googledomains.com. dns-admin.google.com. 1342179275 21600 3600 1209600 300

;; Query time: 46 msec
;; SERVER: 164.100.3.1#53(164.100.3.1)
;; WHEN: Tue Oct 25 10:55:30 2016
;; MSG SIZE  rcvd: 101
Kansals-MacBook:~ Kansal$

Hope this helps!!!