Both are excellent products! Either of the two will meet perfectly, in the end it is a matter of personal satisfaction.
Fact is that Emsisoft has a non-standard customer service, the best service I have seen to date!
The user-friendly interface of Emsisoft influences a lot also in my decision, the G-Data as excellent as it is seems abandoned, and this gives a bad impression.
In tests against ransomware Emsisoft is more solid.
Emsisoft allows use together and that's awesome! On my computer today I make use of: Emsisoft + ZoneAlarm (I do not use the antivirus, only the firewall) + Zemana AntiMalware (Reinforcement) + WindsCribe VPN.
Emsisoft has a function that protects the windows firewall, and this is very interesting, the windows firewall is excellent but it is very flawed when it comes to viruses or malicious applications, this is why a virus can manipulate the firewall without difficulties and this makes the windows firewall be flawed, Emsisoft protects the firewall, blocks changes.
I use ZoneAlarm because it is excellent, complete in terms of firewall, protects the system with the default input filter and even makes an analysis of the programs in the output filter, preventing software without provenance or viruses from connecting to external environment.
ZoneAlarm when installed gives the option to install its antivirus function, but I do not recommend it because in addition to being more basic causes slowdowns on the computer.
But basically if you make use of Emsisoft is already well served, the windows firewall in this case will serve you!
Emsisoft is enough on your computer.
I would recommend for example Kaspersky free + ZoneAlarm Firewall, but unfortunately it is not a combination that works, anything installed next to kaspersky causes problems on your computer, kaspersky free alone is good against viruses but does not protect the firewall (which is normal, only Emsisoft protects), and sometimes kaspersky itself turns off the windows firewall, anyway, kaspersky free only even in the last case because the windows firewall with it will not work well.
Any other free antivirus works well with the windows firewall, but it will not protect it, this only Emsisoft does.
A reasonable solution would be to acquire an antivirus that already has a firewall, kaspersky itself for example, but due to its report and the political issues of the country, I recommend you use Emsisoft and if you want (it is not necessary) put next to it the ZoneAlarm Firewall.