I was recently in the market for something very similar, so I can at least tell you why I
didn't buy a Surface.
First, the specs were too inflexible. I wanted a machine that can handle some serious coding, and for me that means running Eclipse, on Linux, inside a VM. For that to work well, I need to be able to give the VM 4 gigs on its own, so the host needed 8. The Surface tops out at 4.
Similarly with hard drive space, I want to be able to keep a couple of VMs around, install several large games, and take music and movies on trips. Now, the Surface has an SD slot, but the internal drive tops out at 128GB, and Windows takes something insane like 50GB for itself. So while music and movies could go on a card, that increases the price and adds hassle.
Also the CPU and Graphics chip are both last-generation. Not only does this mean lower performance, but also worse battery life.
The second big point was the keyboard. The basic keyboard is goddamn unusable for touch typing, and even the pro keyboard is terrible. The travel and response of the keys is not good, the layout has several weird choices in it (just look at the arrow keys), and the touchpad is small. I was looking at this as a serious laptop replacement, and having a janky keyboard just wasn't going to fly.
At the same time, the keyboard is just loosely clipped onto the body. So you can't actually hold the thing on your lap AND use the keyboard well. You HAVE to put it on a table or something, and you can't adjust the angle of the screen so god help you if there's any glare, or your chair is the wrong height.
What I ended up getting was this
and I'm very happy with it. 8GB RAM, 256GB SSD, newer generation chips so better battery and performance. The keyboard is much nicer in every way, and since the screen has a real hinge it's a laptop that actually works on your lap. The only tradeoff is it's slightly thicker in tablet mode, but since at least half my time will be spent using the keyboard it's well worth it.
Honestly I was sad that the Surface wasn't better. It seems like Microsoft has an incentive to sell better hardware for cheap to grab some market share, but there were just too many compromises on specs and design for it to be attractive.