This is a rather open ended question. This "field" is developing at an alarming rate. I guess it all depends on what you want out of it and what you want to put into it.
I recently purchased a 3D printer, and here was my thought process on my decision.
For me it was between the SoliDoodle 3 and a Pursa
Build vs Ready to run: I liked the allure of taking the thing out of the box and using a tested system, particularly for something that I had never used before. I also like to build things and see how they work. IF I see how they work, it makes it a lot easier for me to troubleshoot.
Build materials: What is the thing built out of? I really like the fact that the SoliDoodle is made from metal. But I built a CNC mill about 4 or 5 years ago out of MDF, and it is still working great, and at times gets a fair amount of use.
Able to print from SD card (No PC needed). Is it important to you that the 3D printer is not tethered to a PC? I have a rather old PC and didn't really want to be tied to the PC during a print in-case it froze or got bogged down. I have read stories where PCs would freeze/screen saver would kick in/auto-reboot after updates, etc would wreck a long print job. Not sure how often that really happens, but something to be aware of.
Well there are a bunch of other things to consider, but for me those were the top 3.
I ended up going with a Pursa. I don't want to say which one here as this is a SoliDoodle forum, but I must say service after the sales has been top notch. A++ for sure.
I built it myself which was rather easy, and nothing out of what I was expecting. Maybe took 3 or 4 days to get it going, but I took my time, enjoyed the build making sure everything was right. I was able to dial in the X/Y axis in on the 2nd try as the default out of the box firmware settings were darned close. Working on the Z/extruder now, but it must be close as the prints I have made are just fine. The one I built was a wooden case. I would have preferred metal, but for cost/benefit for me wasn't there as by the time I wear the wood out, I'm sure I'll be wanting a bigger/better/newer 3D printer anyway. Also there isn't the stress on the parts on a 3D printer in the way that there is on a CNC mill, and it is holding up just fine. I love the printing from SD card. Just dial it up, and let it go. Thus leaving the PC free to do more drawing ;-)
I have about $200-$300 less in my printer than the SD3, but I had to build it myself,(which I like, but get that some folks don't) and had to source a few of the parts myself.
Anywho, that's kinda how I decided, and so far I am very happy with my decision . The SD3 was a very close 2nd.