It's overwhelming, isn't it?! So many choices and information and advice coming from all directions. I can only share what I've learned from 13 yrs. of road biking.
Brand: All brands make good bikes. The more expensive the bike, the better it generally is. Money really does buy you something measurable on a road bike. Better frame materials, better components, better wheels, better tires, better...
Frame material: Aluminum is the cheapest, usually, and thus is found on most "entry level" bikes, and it's a harsh ride. If you haven't ridden anything else, you'll think it's great until you take a test ride on something carbon, steel or ti. Then the aluminum bike suddenly feels like a tuna fish can. Steel has been around forever and it is the most comfortable, but it can weigh in a bit heavier than some of the spaceage materials. Titanium is light & responsive, but has fallen out of fashion in the face of carbon. I am way too heavy to ride a full carbon bike, so mine is a combination not found in the US - steel & carbon. Bikes here are aluminum & carbon. If you are of normal weight and can afford it, carbon gives a very sweet ride. If you are overweight like me, carbon is overkill.
Components: Big payoff here for extra $$ spent to upgrade. I have no preference between Shimano & Campy. I have both. But I've had lower end components - Shimano 105's, for instance - and there is a definite benefit to having the upgraded versions. Shifting is dependable & seamless at the high end.
Fit: I have to share my fit experience. In the US, a good bike shop will put you & your demo bike on a trainer and measure all sorts of things - leg length, torso reach, seat height, crank length, etc. etc. Then you buy the bike and spend the first year tweaking the thing to correct little problems, like the handlebar stem being too long or too short and the seat height not being jussstttt right. I fell in love with Scapin bikes on a trip to northeastern Italy. I went to the Scapin bike shop, where no one spoke English, to be measured for a bike. They looked me over, pulled a bike off the rack and motioned for me to straddle it. They looked me over again, had me get up on the bike while they held it in place and peered hard from different angles. They made some notations on a bicycle order form that had a graph of a bike frame at the top. I came home with the paper & a dream that one day I might go back for a bike. Three YEARS later, the opportunity came, and I faxed them the measurement sheet they had given me. In halting Italian/English, I ordered a custom bike to be painted tangerine orange, for pickup on a specific date. I was nervous! What if it didn't fit? What if it was all wrong? Guess what - it is a perfect fit. I've ridden it for 5 years now and haven't changed a single thing. The Italians know how to make a bike! It is an interesting combination of steel & carbon, beautifully crafted.
Flying: Do not put much hope in flying with a bicycle in, or to, the US. Almost none of the airlines will accept a bicycle now, unless it's a folding "Bike Friday". They have modified their weight and size restrictions such that it is impossible for a bike to pass their rules. Delta still allows SOME bikes, if you can pack them down small enough, at $300 per bike, per flight. I am not kidding. Check their websites. I can no longer take my bike to Europe, so I'm not going.
Fun: This is THE most important factor. Keep test riding some bikes. A good bike shop will let you take it for an hour or so - usually if you leave your drivers license or a credit card - and allow you a chance to really feel it out. You will get on a bike eventually that just sings, and you'll know. Perhaps it's the pretty paintjob combined with the good components, or perhaps it happens to fit you to a T. But it will feel like FUN. That's the one you buy! Then ride the hell out of it - and don't compare what you have to everyone else - just ride, ride, ride. It's pure joy.
Good luck to you and we want to see a photo when you've made your purchase!
Mary
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I've never met a hill I couldn't walk up.