My recommendation after owning all three would be the 1400c and the 2300c. The 3400c is notorious for failing as already mentioned, and 8.6 on a 1400c with 64MB RAM is perfect. As it is the 117mhz model you can easily find a 133mhz to speed it up a bit.

The 2300c gives you the small form factor with the dock option should the LCD ever really crap out. The 2300c would be best with 7.6.1