They are all great bikes. It is very difficult to to recommend a brand. There are also variants of honda and suzuki that you did not mention that will also fit the bill. It comes down to your budget and what you want to use it for. Is it for everyday use? Or Is it a recreational vehicle that you use on weekends. Why don't you buy a used bike and see how it goes.
GS 150 is a big heavy touring bike meant for long routes, it's quiet and comfortable. The biggest flaw of GS 150 is its size which makes it hard to move through thick traffic.
CG 125 has good acceleration, good sound. It was built for short trips within city but on long routes they are uncomfortable due to vibrations and seating position. They are also not stable on high speeds. They are also favourite of theives and are mostly snatched if you live in karachi.
YBR 125 is new entry. There are few service centers, expensive spare parts. It is yamaha's desperate attempt to break monopoly that honda has in 125cc category. It has less acceleration than a honda cg 125 but people who own it like it.
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