I've had both. Two Daystate Wolverines, Two FX Royale's, and a Bobcat. If I'm picking one or the other right now today, it's going to be FX. The versatility their platform offers to the user to be able to adjust and fine tune for accuracy, across multiple calibers in such a friendly way is currently unmatched.
Pros for Daystate:
1.) Beautiful. Stocks are simply gorgeous. Arguably the most attractive wood stocked traditional rifle on the market today.
2.) Fit and finish are top notch. Match grade triggers, generally very quiet with Hugget shrouds, magazines are very robust.
3.) Longest manufacturer warranty in the business (that I know of)
4.) Anti double load feature on many of their guns
5.) The electronics in some of their guns, I've recently learned, can offer some intriguing features that will be pros for some but possibly cons for others. Examples include the electronic trigger, solenoid cocking, etc. I think electronics are personal preference more than a bad or good thing.
Cons for Daystate:
1.) They tend to lag as a corporation when it comes to bringing desired features to market. (Air Arms tends to be in this boat as well) Only recently have Daystate announced they'll be producing a mechanically regulated gun with a side lever. These desirable features have been common in the market for many years with other brands.
2.) While at least as reliable as any other brand, I also don't think they're any less prone to having issues than any other brand. Both of my Wolverines had internal problems that I couldn't fix and had to be sent back for repairs.
3.) Until their new "R" models are released you can only get electronic regulation which tends to be on much more expensive models.
4.) Pricing. Daystate are among the most expensive guns out there and the true value of anything is determined by how much someone is willing to pay. That being said I think a strong argument can be made for the fact that paying $3k for one of their flagship pieces isn't going to yield you any more accuracy/precision/consistency than a lot of guns half the price.
5.) Unless you pay up for an electronic model, the options to adjust the power, particularly for the layman, are very limited. No transfer port adjustments, etc.
Pros for FX.
1.) I don't think anyone can argue that they are the most innovative airgun company around today. Not only are they the most innovative, but they are really good at being innovative with things that the general population really wants. Additionally they bring these innovations to production much faster than any other company.
2.) Fit and finish are top notch. Smoothness of side lever action is second to none, match grade triggers, generally very quiet, power adjustments are very repeatable.
3.) Smooth twist and smooth twist x barrel. HUGE advantage of being able to change calibers and twist rates. Also with the new barrel liners you can apparently do so rather inexpensively. Some of your FX guns can be a .25 hunting rig in the morning and a .177 plinking rig in the afternoon. That just doesn't happen with most other brands. I won't go into the other smooth twist benefits here. There are a few and they've been covered ad nauseam. A google search will get you all you need.
4.) They are currently the only company offering guns with such adjustability. I don't know of anyone else that offers a transfer port adjustment, hammer spring adjustment and regulator adjustment all externally accessible. This infinite adjustabilty goes a long way to letting the user ring out every last drop of performance that they can out of the gun.
5.) Pricing. They've made an impressive attempt to get high end features on their guns while staying below the $2k threshold. I think it's arguable, especially with the new Dreamline series, that FX offers a strong "bang for the buck" lineup. More importantly they do so without compromising quality.
Cons for FX.
1.) The speed of innovation and bringing new ideas to market so quickly can result in some models having "growing pains" as the bugs tend to be worked out over the first production runs.
2.) You currently have to get on a wait list to order some of their more desirable models as they aren't so easily able to keep up with demand. I'd call this more of a back handed compliment than a con but it's certainly a con if you want one in your hands right now.
3.) Their stocks, while very functional and attractive in their own right, are not as eye popping as the stocks on the Daystate rifles. In my opinion anyway, I guess this part is subjective.
I'm genuinely not trying to be a fan boy, I just legitimately can't think of any other cons for FX. I'm sure others will chime in. There are lovers and haters on both sides of the isle here.
All the best!
Cliff