Well, I have the 305 and 'er Indoors has the 205. The only difference is that the 305 has a heart rate monitor. The 205 doesn't support HRM but the 110 can.
The 205 is larger than the 110 and has more features, such as advanced workout support (intervals, structure, and so on). The 110 is pretty much the same as the Soleus but with the advantage of being able to download your data to Garmin Training Center, Garmin Connect, Runkeeper, and so on. That sort of thing is very useful.
So, of the two I'd pick the 205.