Any bike is good, so long as it fits. There is something better about a bike that is "yours." A better-fitting bike, with good shorts, seats, and shoes, will be more comfortable for longer rides, and a bit faster.

If you think you are riding too slow, add some "intervals" to your ride. If you are using a cycle computer, you have a pretty good idea what your average speed is in a given area. Raise your speed by 5 mph (or 8 kph), for 30 seconds. Then slow down to your usual speed. Do this a few times, and after a week or so, increase the time to 1 minute. If you do this for a few weeks, you'll find that you can lift your average speed significantly.

Another thing I recommend is joining a group ride. It's fun to ride with others, the speed is higher, and you can drop out at any time. Faster riders tend to group together and ride away, average riders group together and ride at a moderate pace, new and lower riders group together and ride at an easier pace. Group rides are a good way to meet people and make friends, and to motivate you to get out and ride on weekend mornings.