I always prefer CLI, because each command gets a complete and meaningful response, so you can (often) understand what's going on. When something goes wrong with a GUI, it's hard for me to understand if there's a problem with the system or with the GUI itself.
Of course, in my little experience, GUIs played a relevant role in the diffusion of linux systems because they make complicated or complex tasks easy even for newbies; we've all been newbies and we'll always be newbies in one field or the other.
Anyway, in my opinion, CLI is often more reliable.

CLI

Being a still pretty much wet-behind-the-ears newbie, and having come from a background of years of Windows use, I'm still more comfortable with using a GUI, but that doesn't mean I think the CLI isn't important, or that my preference might not change down the road, with more comfort and familiarity with Linux. I do find myself often wishing for a "Command Line list of commands and what they do in plain English (or whatever one's native language may be) for Dummies"! Hopefully, the Ruby training I'm making my way through now will help some, with more relevant trainings awaiting me down the road, like some Python... maybe a little Perl...

For 'non' linux savvy people like myself I'll say GUI in the first instance then subsequently CLI after gaining a bit of experience.

Generally the GUI. A good GUI is self documenting, just hunt through the menus and forms until you find the right option.
CLI and configuration files are fine if the documentation is good enough to find and understand what you want to do.

For instance I've been tasked with a postgresql 9.3+ install on RHEL 6 2 node cluster with streaming replication to another 2 node cluster and I've spent the whole of last week and yesterday to try and find something online that can assist me with the deployment based on the fact that I'm a SQL Server DBA with little or no knowledge of linux and only had experience of installing postgreSQL on a Windows server. A guide to do this via GUI or otherwise will be nice but sadly haven't found anything concrete unless I'm not looking in the right places :-)

I can only install distros using GUI, but I prefer command line for sorting and moving files around, creating directories and doing searches etc. I usually add new software with the command line (apt-get).

GUI when I can, but I notice that some distros are forcing somethings to be only done via the CLI.

I had only been using Linux for about a month at home when I started a new position at my company being a Red Hat admin. At first the GUI seemed much more convenient, but being that we use an extremely locked down version of SELINUX on our systems, I found that the GUI often times wouldn't work and I had to use the command line for most actions if I wanted to get something done. Which is fine by me, because it helped me learn the command line much quicker than if used the GUI for most things.

It is because they're still a newbie or that they've only posted like 2 or so times?

GUI: The Rhumatiz, doncha know!

There's not really an option in this poll for me to accuratly answer. It entirely depends on the task I'm working on. Most frequently it's a mix of both, there's some things where GUI is vastly superior and other things where CLI is vastly superior for my day to day working and use.
I was doing data recovery off a drive a couple days ago, I added the broken and a good drive to backup the data to. While the tool I primarily used was CLI, it was a GUI partition manager I was using to quickly find which drive was what, and to browse the backed up files and make sure they didn't recover as just garbage, since it was a lot of photos and videos.
When it comes to desktop side, it really does depend what I am doing, because the GUI tools are sometimes easier and quicker to do thing with, and other times CLI is the faster way to go. Overall I do use the CLI more frequently (probably 2/3 of the stuff I do administratively), but it's often blending both.

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FWIW Synaptic is a Graphical User Interface, GUI

Hello there to all the Geeks!!!

I Prefer the Command Line but for some things!, a GUI is a better place! Thank you and, i think, we have to do the job and all of the Apps on LINUX have a GUI even if WE do otherwise. Some people, new people, they have not the skills for some things! WE have to Introduce on a GUI before the Command Line.

Perhaps I am being a bit grumpy today but it seems to me that many answers to this question (mine included, to an extent) are not answering the question:Emphasis mine.
Of course we generally prefer a GUI to a text-based TTY for watching videos, even to check (sorry, just an example, no offence to those mentioning it).

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