Karakol sits at the far eastern end of Issyk-Kul lake, roughly a 6-hour drive from Bishkek along the lake's northern or southern shore. Most travelers choose between three options.
The cheapest option, departing from Bishkek's Eastern Bus Station once the car fills up (usually 4 passengers). Inexpensive, but timing isn't fixed and comfort varies by driver and vehicle.
Runs on a rough schedule from the same station. Cheap, but slower and less comfortable for a 6-hour ride, with limited luggage space.
A private car door-to-door, at a fixed time, with room to stop for photos along the southern shore of Issyk-Kul (Burana Tower, Chon-Kemin valley) if you'd like. Priced per vehicle rather than per person, so it's often comparable to shared options for a group of 3-4.
If your schedule is flexible and budget matters most, shared taxi or marshrutka work fine. If you're arriving tired from a flight, traveling with family, or want to add a stop, a private transfer is the more comfortable option.