Timo alerted me to this thread. We use a DJI S800 EVO for higher end jobs, and a Phantom 2 with GoPro for our clients on a budget. I also have a Blade 200QX as my "fun/practice" drone, and have seen a few of the 350QX's fly. Here's my take on each:
Phantom 2: Fit and finish is better than any other RTF drone I have seen in it's class. Ours has been very reliable, is very stable in flight, and makes an excellent camera platform. The Vision+ offers a very simple and elegant aerial camera solution, and you can use an iOS device or tablet as your FPV screen. However, the video is not quite as good quality as that of a high end GoPro, which is why we use a GoPro with Zenmuse gimbal. If you go the GoPro route, you will have to also buy a video downlink, dedicated FPV screen, and an iOSD unit (this is all built into the Vision+). I should also mention I absolutely love the battery solution that DJI uses. They use a 5200mAh 3S "smart" battery that is easy to swap out, and gives incredible flight times.
350QX: I've seen these fly, and have tons of stick time with their little brother the 200QX; they are fast and agile compared to a Phantom with stock settings. Their flight characteristics are not quite as stable, but if you have RC heli experience you shouldn't have any problem. I don't know much about how they perform as a camera platform, how smooth their gimbal is, and what quality their video is, but I have heard even the QX3 isn't quite as good as the Vision+. Don't take my word on that last statement though, that opinion came from only one person who I talked to about it.
Yuneec: I know nothing about this drone, in fact I didn't even know it existed until today. One thing to take into consideration, which I'm sure you already know given your heli experience, is that availability of parts is important. Most hobby shops carry Blade parts, and there are many drone shops across the US that carry Phantom parts. This may or may not be an issue for you depending on how you fly... I've been operating my business since Jan 2014 and have never crashed any of my drones, so I have never needed to buy spare parts.