Very interesting read. This is my experience, Been commuting daily for the last few years from Eastwood to Parra... approx 24-30km round trip depending on route.
The bikes I have commuted on include...
04 Giant VT3 dual suspension with 700C rims and 28C tyres
Review: To heavy and slow on hills, too much bob, generally, DON'T get a dually for commuting. Ended up wearing out the drivetrain from it and had to replace everything. Why did I do it? I was getting back into riding and had a bad back. The upright position with cushy riding just made it pain free but not helpful with speed or efficiency.
96 Apollo Himalya with 26x1.3 ContiContactSports/Specialised Fatboys, EA50 stem/bar/seatpost, racks/panniers
Review: this has done most of the mileage and is now awaiting a rebuild. The rims are worn from braking, hubs are buggered. I rode in rain or shine. Overall, hardtails are great for commuting because they are very robust, upright seating position and great for racks. Lockout fork is a must for road riding... so I went from a RST381 fork (which was pretty much useless) to a Manitou R7 Super with remote lockout. Upside? Robust, can jump gutters, super stable, amazing pick up at lights, quick handling... Downsides?... heavy, geometry not ideal for standing climbs, 26inch wheels roll slower, stiff, Alivio 21spd doesn't have the topend
'06 Giant CRX1: commute with this bike now and got 2 wheelsets, R550s (11-23 cassette) with MichelinProRace for weekend rides and R500s (12-27 cassette) with ContiGatorskins for commuting. Runs compact cranks 34/50.
Review: I love this bike. Initially, the angles were quite steep compared to my mtb but I got used to it. I've added ski bar ends giving me plenty of hand positions without needing to bend down any further, also can quickly access brakes and shifters. I found the ride is very dependant on the tyres, with 28C, it gives you a bit more security and cushioning but not losing too much speed but I still love the pace of lighter wheels for weekend fast rides. I think it is a very versatile bike. The frame is virtually identical to the OCR but a little stronger and more room in the rear stays and more robust/fogiving fork. Also, you have eyelets which anything from an OCR1 up doesn't have. The Vbrakes are much more powerful than the road brakes. I go on many group ride, hilly ones up to 100kms and it is fine keeping up with the roadies. You won't be in a the lead but you can certainly keep the pace. Apparently the build is strong enough for light offroading. Pros: Fast with control, still not as fast as a drop bar but close..... Cons: a bit flashy to be parked around, can't jump gutters at speed, not as stable as the mtb.
04 Giant Elwood: This is the wife's bike, when I now commute a short distance and don't bother with cycling gear I choose this bike. Essentially, it is only good for up 20km/h crusing around. The Altus level gearing is ****, and upright position is hopeless for building up speed or climbing with any pace. The suspension forks are so flexy, I am not game to corner at speed. Pros: supercushy for short distances, park it anywhere cause it is only $350. Cons: weight, quality and so on. Make sure you get something at least Deore/Tiagra level if you are using the bike seriously.
I also have a DMR trailstar but DJ bikes are at best only good for offroading
I have ridden my brother's TCR1, great pace but too harsh and the angles are too severe for my back. Also my gut touches my thighs when I ride on the drops... SO, you can imagine how fat I am
For commuting and non competitive riding, I would definitely go a CRX2 and up or a OCR 2. Of course there are other options available in the other brands but it is too hard to recommend when I have ridden them.