First I should let you know that I work for Saltire Software which helped Casio on the ClassPad project, so I have a special interest in the ClassPad
I have also worked with both TI and HP and like their calculators too.Personally I like the ClassPad because I find it much easier to use, which makes it much more powerful. The ease of use isn't just because it has a pen, it is the way it uses the pen. I can open up an eActivity and insert a geometry strip. From the eActivity I can solve an equation and then simply select it with the pen and drag-and-drop it to Geometry to quickly graph it. I can then do some transformation on it and drag it back to the eActivity to get it's new equation. I can then use that equation for some additional calculations. As far as geometry, the TI is useless without a pen. It is painful using the arrow keys.
Another feature I like on the ClassPad that I don't hear mentioned much it the "Main" (i.e. "Home") application. Unlike other calculators which only give you a fixed history, on the ClassPad you can actually scroll up and edit any expression in you history. The ClassPad will then recalculate everything below it.
The spreadsheet for the ClassPad is also excellent. I is the best spreadsheet I've seen for a handheld.
I think of it as comparing DOS to Windows (although it isn't really that drastic). What would you do if you couldn't use a mouse in Windows but had to use the keyboard for everything (it can actually be done!). After using my ClassPad it find myself trying to tap on the screen when I ever quick to the TI;)
On TI's behalf, the TI-89 is faster evaluating some expressions, although that might change in the future
. It also has a nicer version of BASIC for programming. The TI-89 has units as a built-in object, although I've seen an excellent units package written for the ClassPad by a user.
