The biggest source of buyer's regret isn't a bad bike — it's a good bike bought for the wrong kind of riding.
A mountain bike (MTB) is built around suspension, wide knobby tyres, and a strong frame for rough, uneven terrain — unpaved trails, gravel, loose ground. That same ruggedness makes it heavier and slower on smooth tarmac than a bike built for the road, so it's the right choice if your riding actually includes rough terrain, not just because it looks capable.
A hybrid sits between a mountain bike and a road bike — an upright riding position, moderate-width tyres, and usually no suspension or only a light front fork. It's the practical all-rounder for mixed city riding: paved roads, the occasional unpaved patch, daily commuting and errands, where you want comfort and a manageable weight more than off-road capability.
A roadster is the traditional upright city cycle — simple, durable, low-maintenance, built for flat paved commuting at a steady pace rather than speed or trail capability. It's often the lowest-maintenance option of the three and a common choice for straightforward daily commuting on city roads.
If most of your riding is a daily commute on paved roads, a hybrid or roadster will usually serve you better and cost less to maintain than an MTB bought for terrain you rarely ride.