Go with a Desktop if you can go for periods of time without a computer and want more power, but go with a laptop if your always on the go and need a computer for work and personal uses.
I have noticed that laptops these days now have the same processors desktop have. I know A desktop that has an i5 Core while my has a i3. There are some laptops that can run the i5 chip.
I just went and bought a Apple MacBook Pro 15" with Retina display, cost me a little over $3,000 AUD but well worth it..
A bit pricy considering a windows laptop with similar specs would've been around $500 cheaper, however for what I require it for, the MacBook is the best system, plus everything just works out of the box..
However as you've already got a tablet, I would buy a desktop.. Better yet, I'd personally build my own, go to umart.com.au, they've got fantastic parts for fantastic prices..
And there's one almost everywhere depending on where you live.. QLD, NSW and VIC are covered..
I'm using my laptop as A desktop its connected to the monitor and instead of using the WiFi I am using Ethernet since Ethernet sends data more secure. If I ever need to take it any I can easily disconnect it and use the touch screen. (obviously with the mouse & keyboard)