Important Factors, Assumptions
This answer is going to totally ignore all the groundwork needed before a species can even dream of space travel. We're going to assume some intelligent form of life evolves on Titan, and that they want to get off of their moon and explore all the things in their sky. (Which they wouldn't know about, because Titan's Atmosphere is opaque at many wavelengths.)
- An escape velocity of 2.638 km/s (compared to 11.186 km/s for earth)
- A mostly nitrogen with some methane (1.4%) atmosphere
- A smattering of other chemicals (such as hydrogen, hydrocarbons, etc.)
- Higher surface pressure of ~1.45 atm.
- A Surface Temperature of ~94 K; that's cold. Cold enough to store liquid gasses.
Here are some demonstrated to work rocket engines they could use:
It should be noted that these are just a few rockets which are possible. There are many types of rocket these aliens could go for. The significantly lower escape velocity means that they have more options practically open to them.
Getting the liquid oxygen oxidizers, which many chemical rockets require, would be hard, but not prohibitively hard. They could decompose the water they have to make the hydrogen-oxygen rockets. Furthermore, they can store them on the surface without needing coolant. They could grab a bunch of air to power their steam rocket. This also ignores the other nifty rockets out there, such as light beam powered rocket or nuclear gas core rockets. There are other ideas, too, such as scramjets, which they may take advantage of to get to orbit.
Really, it seems the aliens in question would need to answer: what rockets do they feel comfortable with? They have options, and can easily choose between many of them. Sure, Titan itself presents problems, but they can be overcome.
What about that Atmosphere?
According to Robert Zubrin, if you found yourself on the surface of Titan, you could fly by attaching wings to your arms and flapping. Flying is not as energetically difficult as on Earth. You could easily have a craft get into the upper atmosphere and then use the engines to get into orbit or achieve escape velocity. So yes, you would not want to rocket your way from the surface to orbit, but you could easily fly up to a point where it would make sense to rocket out. You can hear about the Cassini-Huygens mission and some of the challenges presented by the atmosphere in this presentation by Elizabeth P. Turtle.
I suspect the thicker atmosphere mostly means that launch vehicles will simply fly up through most of the atmosphere, and then launch a payload into orbit.
Rocketry on Titan is Easy
The thicker atmosphere makes getting higher up easier, and the lower gravity makes escaping that atmosphere easier. You can synthesize oxidizers from the ice, or use one of many other rocket options to get out. The cold surface temperature even means that fuel containment tanks need not be cooled, and that's further energy savings!