Hey Pat,

I commute every single day, multiple times a day and only by my bicycle, so I can tell you that finding the right bicycle is very important. I used to commute on an old steel retro schwinn from the 80s. It was a great, fun bike, but when I upgraded to my aluminum frame and carbon fork XDS road bike, it made a huge difference. Since other folks are talking about weight, I'll chime in. Weight makes a big difference when you're riding every day. Sure, you can have a heavier bike and pedal harder, but a lighter bike is going to help you strain less during commutes. Ask an avid runner about shoes and they'll will emphatically tell you that shoes makes a huge difference. It's the same for bicycles.

If you're 5'8, here is your sizing chart:

Road Bike: 52-54 cm (I'd go 54)
Hybrid: 52 cm
Mountain: 17"

If you're looking for a great bicycle within a budget, check out XDS Bike Co. They have great bikes and ship for free. Their hybrid section is growing and has bicycles for all price ranges and qualities.

I recommend this one because I've ridden it and loved it:
Cross 300: Cross 300 - Hybrid Series | XDS Bike Co

But this is a very affordable bicycle that will do the trick:
Traveler | XDS Bike Co
They don't have the specs up, but I'm sure they will soon.

Anyway, I hope some of this was helpful. I'm a huge advocate for commuting by bicycle, so I'm excited you're getting on board. I don't think you need to spend tons of money, so check out XDS and use the money you save to get all the commuting equipment you want!

Cheers and good luck!
Spencer