I have owned both. Suzuki GS150 2013 model and a current owner of a new blue YBR.
I've completed 6000 kilometers on the Suzuki and have completed 1000 kilometers on YBR. In my opinion, if you want performance, go for GS150. However for everything else, go for YBR.
Choosing YBR or GS150 for touring is bit tough while keeping in mind that the average commute speed would be around 80 to 100 km/h as this is the average speed what people usually maintain which both of he bikes are capable of doing without hiccups.
However, trust me when I say this - the sitting position of YBR is lot better and you'll never feel tired. On the other hand, GS150 has better upright sitting position so you can sit up-right.
If you have a pillion with you, he/she would prefer to be on GS150. The pillion position for YBR is not that great. However, if pillion rider tucks in his legs, he might feel way more comfortable on YBR. Sadly, the fact is, not every pillion rider attempts this sitting position on a bike.
I never cared about fuel average, its dirt cheap now a days anyways, but to some people, it's a important factor in this case, YBR will get a vote. On my trip to murree from Islamabad on GS150, my average per liter was 31. On Ybr on the same route with the same pillion rider, my average was 37.
Anyone who has been to any road trip on a bike would know that at least once in a day, you'll come across a situation where breaking power matters the most in order to avoid an accident. In this case, YBR again get a vote.
Furthermore when on highway, one often find the need to accelerate from, say, 70 to 80 km/h speed to 110 km/h for over-taking, etc. In this case, GS150 clearly wins though YBR is not slower by any means.
Ride 10 kilometers or more straight on rough and tough road on 70+ km/h speed and the rims of your bikes will bent in no time and your bike will start wobbling (especially if you weight over 80 kgs), it just ruins the experience and purpose. Here YBR again wins since it has alloy rims.
On a long road trip, experienced touring guys will tell you that when strong winds come your way, you'll feel the need to reduce the speed in order to balance your ride. GS150, as it is without fairings will might pose some difficulties. However, YBR in this scenario shines. I heard almost everyone says the YBR's (minor) fairing is just for show, I always ask them to ride a bike on a windy day and you'll then come to know the benefits of (minor) fairings.
when driving over 70 km/hr and taking a turn, say, overhead bridge or so, you'll need to lean your bike instead of turning for better control of the bike, in this case, I find GS150 a bit better and stable. I can certainly do that on YBR but I was more confident when I was doing this on GS150. A friend of mine says the opposite. I guess, it comes down the driving style and sitting posture.
It's a known fact that GS150's quality is not top notch but it did not bothered me much. During my ownership, I changed a flasher about 3 times and that's it. On the other hand, no one questions the quality of YBR so better quality translate to better reliability on the long roads.
GS150's turn angle is bit wide which I really enjoyed when going to hilly areas near Islamabad. On the other hand, YBR's turn angle is bit narrow that can help you take u-turns in less space. if you know what I mean by turn angle.
Despite 125cc engine of YBR, the gear ratio of YBR is exactly same or perhaps better than GS150. I mean, you go to 30+ km/hr in first gear on YBR and would not feel that the engine will blow. However, on GS150, when you are over 7000 RPM, you'll just love the thrust but when red-lining, you'll do get the feeling that the engine will blow. It's just a personal experience.
The stock tyres of YBR / YBR-G are much better than what is Suzuki is providing in GS150. When buying the new GS150, you'll feel the seat of GS150 is not that soft however it will get soft in a month or two. However in the case of YBR, the moment you'll sit on YBR, you'll notice how soft the seat of YBR is.
I think, I've covered most of the points in the light of my personal experiences. However, I am not an experienced rider or tourer, I just do it for fun.
Hope it helps.