I'll twist the question a bit: what do I like to commute onto?

First of all, I'm somewhat traditionalist but not old fashioned, I ride on bikes with drop bars since 1970 and enjoy touring. My bicycle either has to be rather universal, and I don't want to have more than one style of bicycle. Living in Montréal also means I have potholes to deal with, but not any mountain terrain to ride on.


Frame. I prefer steel and traditional.
Some say that steel is a bit more resilient – I'm not sure – but it's certainly more crash forgiving.
I also like the top tube to be as high as possible. My touring bike has 64-cm (25") frame and I'd love to get a 66-67-cm" frame with a very short seatpost. More room for water bottles on the road.

For commutes, my older touring bike with a 62-cm frame is easier to jump onto (I'm 48 years old), but I can't put 4 large bottles in that frame. Not a problem for commuting, but a drawback when touring.

The older style of touring bikes make great commuters. They have slender chainstays and seatstays which are relatively forgiving of road imperfections. They tend to feel like a noodle when there is a lot of load on the rear rack (ex.: grocery shopping), but widening the frame to 135 mm rather than 126 mm solves that problem quite nicely.

The same comment goes for the traditional fork with a bend at the bottom. The shock absorbing property of that bend is wonderful, and as a bonus, the wheel follows the ground more closely, so one gets more adherence on ice whan with a stouter fork. I feel that riding my old bike with 700x30 tires (or my new touring bike with 700x32 tires) is as comfortable as riding an unsuspended MTB bike (1985-1990 vintage) with 26 x 2" tires.


Suspension or not?

See above. Simpler is better.

Unless one faces extremely harsh conditions, I don't think a suspension is necessary. And it adds a lot of weight.

Stem and handlebars

I really like drop handlebars. For short commutes, I don't hate the old style curved bars that were typical on 3-speed bikes. But, my short experiences with flat bars tell me they are good to give me shoulder pain and wrist pain in less than 15 minutes.

However, I like my bars to be HIGH. The tops are about level or slightly higher than the saddle, which means I need either a long quill or an uncut fork with a high-angle stem.

I also prefer the look of a quill stem, but the threadless one never squeeks. Basically, with threadless, as long as the bars are high and there are 5-10 mm of fork steerer left to raise the bars again, I'm ok. But don't even try to sell me a bike without any height adjustment left.

Gears and shifters

I had single speed when young and felt great when I got gears (at about 10 years old)
I tried fixed gear a few years ago and didn't like it. So I definitely prefer gears, and with an aging right knee, it's more of a necessity than ever.

A single rear derailleur could work on relatively flat terrain or on short commutes, especially if I were solely using the bike for commuting and other short distances. But the triple allows me to find proper gearing on flat terrain and steep hills alike, and whether I'm riding solo or pulling 80-100 kg of groceries (ex.: last weekend).

I prefer the openness of the derailleur system, but know that having 2 shifters is intimidating for many people.

My preferred shifters are bar-end shifters: close to the drops and easy to use, with visual indication right there. My second choice is with downtube shifters and STI come last. I find them hard to use from the drops and really don't like the feeling of levers that move inwards.

Wheels and tires

I'm 1.82 m tall with 90-cm inseam, so I use rather large bike frames. So 700c wheels look nicer than 26". I also prefer all bikes to have similar wheels, so I have only one spare tube to carry in my pannier. No risk of having a 700c tube in the pannier... and get stuck with a flat on a bike with 26" wheels. For me, that's the only rationale between 700c and 26".

Tire with and pattern is a more important issue.
For 3 seasons, I ride with 700x30-35 slicks. My long-time favourite has been Continental Top Touring 700x32. In Winter, I use 700x37 Nokian Hakkapelliitta on the commuter/bad weather bike and 700x37 knobbies (no studs) on the tourer/long distance bike. Let's say I generally don't ride 50-100 km on days with snow storms, icing rain...
Pressure is 100 psi in summer, 70 psi in winter.


Brakes

I don't have any disc brake, but for most of my riding conditions, it seems a solution to a non-existent problem. Well-tuned cantilever or v brakes are equally effective in dry weather and almost as good in the rain. For all-weather effectiveness, however, they need to be well tuned and equipped with Kool Stop salmon brake pads.

Because I prefer bar-end shifters, I don't see any real difference between cantilever and newer v brakes that are fitted with pads with threaded posts (v-brake style pads). I have one bike with cantis (old style, which is a pain to adjust) and two with v brakes and the brake feeling is exactly the same.
Still, minor advantages of v brakes:
- slightly cleaner look (less cable junctions);
- easier to adjust;
- the rear brake doesn't stick out in panniers or into my heel;
- on a small frame, a canti has very little room for adjustment.

So far, I have replaced only one rim because of brake wear.

Drawbacks of disc brakes:
- Need for a sturdier stiffer fork, which makes for a more bumpy ride (we have potholes in Montréal).
- Compatible racks are more expensive.


Other points

Don't forget fenders, rack and lights, preferably all permanently attached to the bike.

For the front, my preference would be for the newer Shimano dynohub with a DLumotec (LED-based) headlight. No batteries to recharge, no bulb to replace... And for the rear, either a wired one (but wiring means more mechanical problems) or the newer Planet Bike Super Flash, creatively attached behind the rear rack.