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.








