2 questions

Is the company providing you with these laptops or did you select the models yourself?

Which surface pro are you thinking to get?

I'm still in the middle of my studies so I don't have much experience from work life, but I'll still offer my two cents!

It depends on the kind of work you're going to use it for. The chances are that a portable device of some sort is the best choice, but if you're absolutely sure you don't need to be moving your PC around too much, a desktop isn't a bad choice either. If you need to be moving it around a lot or have any doubts about it, a portable device is probably better. For most portable situations, a regular laptop should probably suffice, but if you need something that's even easier to carry with you, a hybrid device could be the best choice.

I don't think I've ever heard about there being any technical reasons why any type of device should somehow be a fundamentally bad choice, so it should all come down to your needs. As for the exact device, I don't have time to look into it right now, and my knowledge on components and such is probably a bit outdated anyway so it's probably best to wait for the opinion of someone more qualified on that. :P

I will tell you from my experience that the Laptop with dock is what you want. There is no reason to even consider the other options.

Laptop has the most flexibility. You can bring it to meetings, troubleshoot where you need to and you are flexible with your connection options. Trust me, you will need a VGA port and an RJ45 jack which the hybrid won't provide.

Also you can take it home for standby duty and home office.

Well here is my thinking. Since this is mainly for work, I suggest getting the surface pro 4 Only if it is the model with an i5 + 8gb of ram but at a minimum of an i5. Core M is not very good at handling many tasks and i5 will just be better for the long term and 8gb of ram is also sweet. From the few I have researched, the Surface has the most amount of battery life out of the products you have stated lasting around 8 + hours with wifi surfing. And yes, that is on the i5 model.

http://www.anandtech.com/show/9727/the-microsoft-surface-pro-4-review-raising-the-bar/7

Where as the E6540 will last you 6.5 hours, Dell E5440 will last you 8 but it's display isn't as good, E7240 will last you 4.4 hours, E6330 will last you 6.5 hours. All of them are according to notebookcheck.net

The Surface also has the best display, SSD and plenty of other things. It doesn't have a dvd drive though and it is smaller than the others at 11 inches. So I would say the Surface 4 Pro i5 + 8gb model if your company is paying for all of them. Unless you think you are going to need some of the other things like a dvd drive and etc and don't want to buy usb accessories for them.

Edit: I should mention that none of their displays are as good as Surface Pros

But let's look at it from the IT job perspective though.

Battery life is meaningless. Image quality is negligable, as is size. What you need is flexibility, which is connections.

I work with a Latitude 6530 myself. The keyboard on that is godly btw.

Sounds like you might want a portable device, and sounds like a laptop might be a good choice. You should know yourself whether it's a laptop or a hybrid device you want depending on the exact situations where you need to use the PC, but vivster has good points you might want to consider. You'll probably want a device with a VGA port (or some easy means to provide VGA output, via an adapter for example), and an RJ45 port would be good too. There's a chance you won't ever need them, but there's also a chance they could make your life quite a bit easier. At least VGA seems to be everywhere.

I wouldn't say battery life is meaningless depending on the work he will be doing... Sometimes having great battery life could be a life saver.

The i5s according to the reviews are pretty old but granted can do most if not all office tasks but the Surface also comes with an SSD. And its not like USB accessories don't exist for his needs. If he doesn't want to carry around accessories, I said he shouldn't get it but if he is willing to... That performance will be pretty useful for things like VMs and etc.

The laptop performance is just fine. I doubt he'll be handling many VMs in his job and one running VM should be fine. A laptop is just overall the best and robust package. I don't see a real reason against it while there are plenty for the hybrid.

Also in which IT job do you have to use a laptop consistently for more than 3h without an outlet?

Depends on the situation. If say you have to repair something or you are traveling and the outlet is out of reach and its taking longer than expected, with a Surface, you wouldn't be so tied to the outlet.

We also don't know what he will be running either. Specially considering if he is going to be running an anti-virus, VMs and other things that SSD would help a lot. And its not like Surface doesn't have its own useful stuff that laptops don't have such as the Surface pen which is great for taking quick notes and pictures with the rear camera as well as being more portable. I'd say if he is willing to carry usb accessories for his Surface Pro, it could be more Robust than the laptop

You don't have any reason to get a desktop. Non-gaming desktops are pretty much a thing of the past. You will someday need to take the computer to some meeting or travel and will end up having to use your personal computer and that's not ideal.

Hybrids are flexible, but really useless for an IT guy. Being able to use it as tablet has no use when we, in our line of work, always need to use a keyboard for a lot of stuff. They are also usually not so comfortable. So, any of the regular laptops for the win.

It's a bit harder to talk about specs when I don't know exactly which position you are applying for. But a general advice would be Core i5 minimum (i7 desirable) and lots of RAM and HDD.

Get lots of RAM. 8GB is the minimum, 16GB is the ideal. You may need to use VMs so get some RAM for them.

Don't go for crappy small SSDs. Booting the PC 20 seconds faster or opening apps 3 seconds earlier is great, but most IT work demands a lot of storage, specially if you're planning to develop something. I have around 15 GB of the Android SDK, some GBs of QT, Postgres, huge work files to be processed with Python, PyCharm, a good 5GB for Unity plus a Windows Server VM with Visual Studio eating up a good 30GB. Try to go for 1TB of storage, 750GB minimum. Even if you won't develop anything, consider that VMs are a possibility.