I am the proud owner of a RME Fireface UFX. I can't think of ever using anything else, it is that good. Of course I add other stuff to it for extra inputs, like the Tascam US 20X20, 16X08, and the ART MPII via AES, but the UFX remains the centerpiece of my operation.
 
I operate in a commercial capacity recording full bands with full drum sets, amplifiers, keys, etc... I have plenty of inputs, can send individualized headphone mixes with zero latency to all the musicians using the TotalMix software. I have used all 30 inputs simultaneously without a hiccup.  
 
I love this gear and would immediately replace it if I lost this one for whatever reason. Although if that happened I might go for the UFX Plus next. Bottom line is that I highly recommend the RME line of products. I love them and will never look back.

The only minus point I can think of is the aging FW interface. If you don't mind that, everything else is top notch. TotalMix FX is a joy to use. I even use my UCX with iPad control as a live mixer for a three piece combo (stereo keys, synth bass, kick/snare/2xOH, acoustic guitar and 3x vocals) with three stereo in ear mixes and a FOH mix.

I like mine. Totalmix is a bit unintuitive for me as I'm also using a mixer and it introduces another layer of confusion for things to get routed in unexpected ways, but I'm a bit on the obtuse side. I do get what sounds like solar flares of noise now and then, but I don't think the UFX is causing it. Someone mentioned that disabling wifi might eliminate that. I have yet to do that.

Pragi
 
My question is more based of the future compatibility
for the next 10 years.
Spending  that much money for an audio interface
means to me that I like to have that unit as long as possible.
 

I don't think I will ever need a new AI. But if I do (for some reason), it will be another RME.
RME supports devices over a decade old.
They even updated (firmware for) some older models to take advantage of the "new" TotalMix. 
I cannot remember hearing ANY horror stories about RME ever.

I have used RME for maybe 15 years now.  Used to have a  PCI card thing.  Now I have 2 FF800s.  Low latency (can set to 3ms or so), frequent updates of drivers, supporting of older products.  
 
I have no issues with RME or its products.  They rock.

Sanderxpander
The only minus point I can think of is the aging FW interface. If you don't mind that, everything else is top notch. TotalMix FX is a joy to use. I even use my UCX with iPad control as a live mixer for a three piece combo (stereo keys, synth bass, kick/snare/2xOH, acoustic guitar and 3x vocals) with three stereo in ear mixes and a FOH mix.

This is not a problem at all. I don't use firewire. I am using USB 2 and like I said I can record 30 tracks at once with no problems using USB 2. The UFX Plus can also use USB 3. These devices are not limited to firewire.

Oh sorry yeah I didn't realize the UFX has USB too but then there are no minuses I can think of with that thing. It's a sizeable investment but if you can justify/spare the money I doubt you'd ever regret it. It equals or improves upon almost all alternatives in quality, stability and flexibility.

I have an old FF800 that has never had problems. As others have said its rock solid and they still write drivers for it. Good converters for the price. If my FF800 died I would most likely get another RME interface. -Jim

I (unfortunately) do not have RME interface (yet). But I can write about RME support.
 
I have developed an accessible OSC client (since TotalMix by itself is not accessible) and we have noticed one important option is not available in OSC. We have asked on RME forum and 2 days (!) later there was a beta with this parameter included.

I've had the UFX for years and it's been solid and before that I had the FF400 which was just as solid.  The FF400 is still working well with RME keeping the drivers updated.