I don't really keep up with the latest in the gi game, so I don't know the answer to this question.
which guard is played more these days among the top gi players, 50/50 or deep half?
And which of the top gi players play x-guard exclusively, thank you :) 
Why don't you just watch a few Mundials matches on YouTube?
To make an attempt at answering, though: Deep half is not very common at the moment, but a handful of specialists still make good use of it. (IMO it'll probably make a slight comeback as more people understand how to control the distance from there and connect it with the berimbolo game.)
50/50 is very common, but most times it arises as a defensive tool to stop the leg drag or the berimbolo, rather than as a guard that someone actively pulls in order to attack from. Some players will force the position at times in order to control a dynamic passer more easily, and the occasional leg lock lock specialist may go there willingly. Generally speaking, however, it's not the preferred means of offense of any significant number of top guys.
As for X-guard, I don't think it's a position you can play exclusively, as you need some open guard offense with which to threaten a sweep (spider, butterfly, half etc.) to open up the space underneath the guy. At the moment there aren't a lot of X-guard specialists among the elite, but Leandro Lo plays a modified X-guard position (with a spider hook) a lot.
^ great answer
Bernardo Faria is your man if you are still hanging on to deep half guard but bjj has moved past this as top players learned how to step over to reverse/inverted half guard.
Claudio Calasans plays lots of 50/50.
Agree that Lo is the only current world champion or potential champion playing a version of x guard but even he uses it as a secondary option if his primary double ankle sweep fails
Ok, I kind of consider the double ankle sweep an X-guard position since one of his legs is making a near side X guard hook, but it's definitely a borderline position.
I would say you would see more 50/50 than deep half anymore. I was big on deep half until the mendes bros described why its not a strong position compared to a knee shield half/93 guard. I only started playing deep half again with some of the online instructionals that have came out recently that have crucial details that make the position much better.
50/50 is much more popular, deep half is pretty rare
also nobody plays x-guard exclusively
not so much deep half gward my fren
more fify/fify my fren
Great answers thank you.
What is the most popular guard played by the top competitive black belts these days?
DLR and Spiral?
grillznice - I would say you would see more 50/50 than deep half anymore. I was big on deep half until the mendes bros described why its not a strong position compared to a knee shield half/93 guard. I only started playing deep half again with some of the online instructionals that have came out recently that have crucial details that make the position much better.
Which online instructionals are you talking about?
EddieBravo - Great answers thank you.Only because MG is retired. ;)
What is the most popular guard played by the top competitive black belts these days?
DLR and Spiral?
berimbolo and kiss the dragon my fren
Grillznice - any links to the deep half stuff. I play a lot of half guard so always interested 
Biggy - berimbolo and kiss the dragon my frenThose aren't guards tho, their sweeps from de la riva and reverse de la riva respectively
I play a lot of deep half, and then use x guard to take the back. No 50/50, I feel like I am trapped when I land there.
@Garra and misterw
I've been playing deep half since about 08 and at the time the only instructionals were saulo series 2 and Bruno frazatto bjj super techniques. All were good but entries were always my struggle and there really hasn't been a clear instructional on the struggle between getting beat vs entering deep half. Felipe costa a couple months ago posted a link to his Brazilian blackbelt.com online instructional site and his 6 or 7 videos on deep half gave me tips that I never picked up on In any other instructional. Cobrinhas 3 disc set briefly shows what Felipe talks about but the English translator only describes what he's doing vs why he's doing it. So I would go check Felipe's site. You can try it for a day for free if you use the password TWITTER or FACEBOOK. I used the twitter one a couple months ago and it worked. He promoted the FB password more recently so I'd try that one. And andre Galvaos site who I recently became a member of has some good solid sweeps and tips also on deep half. I considered andre not a guy who uses it but more of a top deep half player that wants to best the position but he shows alot of good stuff on there. Felipe really made me reset the position and like it all over again
^ Ryan hall has a DVD on the deep half also
its amazing how the sport of BJJ has evolved in a different direction than fighting/ mma.. You hear about it all the time with other arts like judo it was a complete system and then went sportive which is cool if its your thing but its really amazing to be living/practicing and teaching at time where the art i teach/train is spreading in all directions gi, no gi, mma.
Cheers dude
@burner22 yes I know about halls DVD but it only came out within 2 years ago. Same with Jeff glovers. Jeff's DVD for me only showed the detail of him hugging the leg with both arms. Ryan's DVD is good and I learned a few things off of it but as good as his explanations are, it doesn't stick with me like other instructors style of teaching.