Hi,
I think that this question can not be answered so easily, unfortunately.
Low-code tools are just a new way of writing applications, and thus, as there is no programming language that is universal, there is no low-code tool that will allow you to build everything.
As a programmer, if you want to do intensive database queries, you will probably go SQL while if you want to write web applications you will probably choose php/node or whatever.
For low-code I think it is more or less the same. Some of them are good at building nice UI (I personally think that Panda Suite is a pretty good tool for that(<a href="http://www.pandasuite.com)" rel="nofollow">http://www.pandasuite.com)</a>) while others allow you do build flows applications or complex event processing, etc...
Everything depends on your needs and on what you mean by "complex".
If there is a low-code product that I love, I would recommend you to have a look at Hackeet (<a href="https://www.hackeet.com" rel="nofollow">https://www.hackeet.com</a>) but it is a biased opinion because I have created it !
So, in order to be honest, I suggest you to have a look to node-red too which seems to be quite popular.
I (obviously) prefer our product but among our competitors, this is the one we prefer.
Hope this helps.<p>Thierry (Hackeet, A Cost Effective Low-Code platform, for everyone !, <a href="https://www.hackeet.com" rel="nofollow">https://www.hackeet.com</a> )