Depends on the way to access the program. If the program is on the web for international cooperation, WI would be better, if we can install it on our pc to work on it individually, GUI would be better.

Hope you can finish and share your program to us soon.

If you share it, more people will be able to give feedback and you can fix bugs faster.

I recomend allways to use web based interface, even on local, all the systems support it and with few changes also mobiles and tablets

I am a software engineering researcher and wanted to provide you some ideas about product design related to my past experiences and research.

You ask what type of interface you should focus on, however, I assume you are asking those you believe will use your tool. If a user is a field researcher, they probably will not suggest a web UI, because they will not have constant connectivity. Others, working in a lab, might like a Web UI. If you narrow down the population of researchers that you want to address first, then the choices will be more obvious. 

Additionally, you indicate technologies such as QT and JSON. I doubt many biological researchers will know much about either of these terms. If you interact with non-programmer users, you might want to focus on the 'features' from a user's perspective. Do they want to use their pc, tablet, or phone to log items? When they log items, do they have WiFi connectivity, or are they in the field? It will help them answer your question more quickly and more accurately.  

As @Gibbs pointed out, it might be useful to specify the options a bit more so non-programmers will be able to understand the pros and cons better.

What I have got so far

I have created a single user model to create, write and manage journals(logs). The data is stored on the disk using JSON files and can be read into RAM for further procession. The journals store the following informations:

The entries store the following informations:

I have created a command line interface that I use to write my diaries.

What means GUI?

If the project uses a GUI toolkit, like QT or GTK one will be able to install it on a PC running Windows/UNIX. The software can be used exclusively on this machine and the program might be for a specific environment, like GNU/Linux.

I am no QT programmer, so most probably this might result in a TK or GTK interface and porting it to Windows might be hard.

What means Web Interface?

A Web Interface (WI) is based on a client-server model. That means, that there has to be a server that runs the backend and a client (in this case anything from Firefox to Chrome) accessing the webpage.

I prefer using cherrypy to create web interfaces, so you would be able to run the server on any machine you have access to, without internet connection.

But you are still able to run a server in the internet or in a local network to make the service accessible. For instance a RaspberryPi with a WLAN module will be able to serve even in the field and you are able to access your journals with a smartphone.

A web interface would be the easiest way to access journals with a Smartphone.

Accessibility in the Field

The web interface would most probably the most accessible interface.

You are able to run it on any Windows/UNIX machine. If you set up an Access Point (WLAN) for your Smartphone you will be able to use it, too.

My Problem

My main Problem is that I am not related to graphics at all.

If someone wants to design the interface (how to display what) I would appreciate some help.

I have decided to use a web interface and add sophisticated offline functionality. This will speed up the development and enable researchers to use the application on virtually any device including handhelds.