TFV4 is great, if you're willing to do a little work. There are certainly many reports of QA issues (cracked/chipped glass, bad o-rings and what have you), but you can get replacements and fix those. The quad coil is marvelous. How smoothly it hits even pumping it up to 120 was quite surprising. Above that I found it a little hot at the end of the draw, but you may find that different.
I don't have the Crown, but from everything I've read that's your best bet if you don't want any hassle. However, the TFV4 if you want to rebuild your own coils (save a lot of money) it's deck is huge making it very easy to use. I can't see anyone complaining about the overall power with the purchased coils. And the versatility of options (single RDA, Dual RDA, Clapton RDA, Triple coil, Quad coil, 6X coil, etc) is just great.
I know I've been having a blast just trying different things on the RDA decks. Dual coil has me going 50-110 depending on how I build it and what I want from it. Single I just built a single vertical coil and it's buttery smooth hits (very excited to tweak and perfect that with some new wire coming in).
Basically if you're looking to screw around with some stuff and build yourself I highly recommend the TFV4, if you're just looking to get a tank buy the coils and have a good vape, from everything I've seen Crown will treat you better. TFV4 if you're looking to get a little geeky, Crown if you want something that simply works (only issue I've heard is that you want to make sure to prime the coils well).