I commute int Tegucigalpa, Honduras, a city with no cycling infrastructure, a lot of hills and a temperature oscillating between 20 and 34 degrees Celsius throughout the year. I Usually ride streets that are wide enough for most cars to leave a space from the sidewalk. I never go between cars. I Also lived for a couple of years in Lima, Perú. Most of the city is flat, and a bit colder. For that I have mostly used a hybrid bike: MTB without suspension, slick tires.
Brakes: V-brakes on aluminum rims or disk brakes. Yes, discs are better but not by much for commuting. I used to clean the rims and pads regularly and had no trouble even in humid conditions. If there was enough water on to cause braking problems, that would mean the street was wet enough for traction to be a bigger issue (as streets are not 100% asphalt, you have to deal with painted surfaces, manhole covers, trash, etc. all of which are treacherous when wet.)
Tires: Slicks are my preferred ones. I use tires marketed for work or commute bikes. They are thicker and harder than racing tires, and they work a lot better on lower pressures, are available in wider sizes and have better puncture resistance for commuting on streets full of debris. For example, I use 700c x 38mm at 60 PSI approx. The lower pressure makes for a more comfortable ride.
Handlebar: I use flat bars mostly because I'm primarily an MTB rider. In Lima I worked as a delivery biker, so I had to maneuver in between car lanes, so I needed a narrow handlebar. Later on, I added some extensions to the handlebar to make it resemble a bullhorn handlebar to have more than one hand position. (I spent 4 hours a day on that bike). For commuting an hour or less, a flatbar is good enough. Rubber grips get slippery with sweaty hands, I solved it with Handlebar tape over the grips of my flatbars for commuting. It's good for cushioning and sweat absorption, so I needed no gloves.
Suspension: None. Suspension adds weight and may not be needed for the route. I do not use suspension, because as I mentioned earlier, I use tires at not so high pressure. If I find a pothole that I can't avoid, I roll over it at lower speed and lifting my weight off the saddle and keeping my elbows at a slight angle, never locked straight.
Frame: My bikes have been rigid MTB aluminum frames, mostly because they are more available and less expensive at least in the mentioned cities. Also they are equipped with mounting points for racks and fenders. In a dedicated commuter or delivery bike, the rack is very useful to carry heavier items, or large items that do not fit a backpack. For example I used to do my grocery shoping on the bike. For longish commutes the rack allows you to carry your items on the bike, rather than on your body, wich helps with cooling and prevents sweat marks and wrinkles caused by the backpack straps or similar. It also helps if the bike has spots to a lock carrier. A good lock is heavy, and it is better to have that weight on the bike and not on you.
Gearing: Singlespeed is OK for a flat route. To climb hills i is better to have gears. If your intent is to get to work and not be tired, you need to be able to select an easy gear for every part of the route. This is a complete topic thoug, I do not want to make this too long.
Accessories: If you will need to lock the bike in a public or shared space, all your accessories should be removable, so you can remove them and take them with you. Otherwise, they are likely to get stolen or vandalized. Lights, phone holders, mirrors, etc. I use little blinking light attached to my helmet so I don't lose time when locking or unlocking the bike.
