GS150SE
This bike got torque. Response is good at any RPM range. Engine runs without struggle. Sitting position is good and seat is nicely designed therefore comfortable. Bigger than YBR. Heard that if maintained, engine lasts long without any overhaul.
BUT overall design is too classic for my taste (Don't like), features don't justify the increased price (therefore normal one is better), bad braking. no good resale.
YBR 125G
Eye catching design, Better build quality than GS150 and SE, much smoother than GS in lower speed, more comfortable and soft ride than GS, Suspension damps the shock much better. Good breaking. Meter has good design.
BUT worst resale, engine don't like to rev high and struggles at high speed, Bad power to weight ratio. Have some weight distribution issue consequently loose stability when braking on slippery surface.
Verdict: I would suggest you to go for YBR G, it looks better, its build better, It rides better in city conditions, its more comfortable and has good breaking power. For me its value for money.