What kind of bike is best to use in Korea?

There's no perfect answer because there's no perfect bike to buy. We all have different budgets and goals. Some of us commute daily while others only ride on the weekend. It's also possible that you're going to ride once during the summer and then sell the bike right back on craigslist where you bought it. No shame in that, either.

Like most things in life, you get what you pay for. Having personally started out on the cheap (<$100) and have incrementally invested more over time (<$1000), I can say that it does make a difference; how fast I go, how smooth gears shift, how comfortable I ride, and how confident I feel about my gear. However, it is possible to sink only a few hundred dollars and be able to keep up with other guys who dropped thousands of dollars on their bike.

Where to buy

Start searching with Gmarket which has low to mid-range bikes, while your local bike shop (LBS) will have much of the same plus service, part recommendations, and bike fittings. To find a shop near you, use Naver and search your neighborhood's name + 자전거점.

You might live near a boutique shop that actually carries mid to high-end models (such as Biclo, Manello, 911Bike, or BikeNara).

Another decent place, believe it or not, is Craigslist.

UK bike retailer Wiggle ships to Korea for free so long as you purchase at least 300 USD worth of products. Not a bad option for high-end gear.

Amazon is a great place to find med-range parts, too. Make sure to narrow your search to online retailers that ship internationally.

My final suggestion is to join up with the Han River Riders on Facebook. Good people, dedicated riders, and lots of great used bikes for sale.

What to buy

Below is a brief guide to understanding some of the different bike types available here in Korea and why you might be interested in one over the other. Thankfully, bicycling seems to be quite popular here, so there's a full range of choices.

Road Bike 
(로드 자전거, 도로용)
- skinny tires
- drop handlebars
- stiff, lightweight frame
- built for speed, aggressive posture
- not ideal for accessories like rear rack or mudflaps
- primarily designed for concrete road use but can be briefly used in the dirt

Mountain Bike 
(MTB, 산악용)
- wide tires
- straight handlebar
- shock-absorbing frame
- built to be comfortable even with excess weight
- primarily designed for dirt paths but can ride on roads just fine

Hybrid Bike 
- a marriage between road and mountain
- skinnier than MTB tires but wider than most road bike tires
- straight handlebar
- ideal for adding accessories
- multipurpose design (commuting, touring, road riding)
- popular choice for new riders

- Folding (폴딩), Minivelo (미니펠로), Fixed gear/fixie (픽시)

From hipster to ultra portable, these bikes are also out on the bike paths. Folding bikes seem to cater to commuters while fixies seem to be aimed at the casual crowd.

Other Considerations 

Regarding Korean-made vs. Foreign (Import) brands, consider that where you buy the bike might also determine where you service the bike. Currently, I ride a GIANT SCR2 that I picked up from BikeNara and have been happy with their service and pricing, for the most part. I used to have two different Korean-made Samchully bikes. Neither were anything to brag about but they were cheap workhorses that got the job done. Speaking of which, a note about frame types:

Steel (강철) - heavy, sturdy, cheap
Aluminium (알루미늄) - lightweight, strong, good value
Carbon (탄소 섬유) - ultralight, fast, expensive

In the end, it all depends on your needs. Currently, I like having a single all-purpose bike that gets me through weekend trips and daily commutes. I know that the correct answer is supposed to be N + 1 where "N" is the number of bikes you own. For me, though, having a commuter bag attached to a decent road bike is just enough for me.

(pictured above: Ibera pakRak Quick Release Commuter Bag 
+ Seatpost mounted rear rack)