I can't say anything about Swype because I refuse to install stolen software on my phone or computer, and all the installable versions of Swype at the moment are unauthorized copies. I have used both ShapeWriter and SlideIT extensively, however.
Each has advantages and disadvantages, as one might expect. The principal disadvantages of ShapeWriter are:
1) It requires somewhat more accuracy in the tracing of words. How much that matters varies from person to person. I've found after several weeks' usage that I can achieve a pretty low error rate without seriously impeding my speed if I pay attention to what I'm doing. I can be a little freer in tracing with SlideIT and still get acceptable results, but it's not a major difference to me.
2) Its treatment of capitalization is idiosyncratic and sometimes problematic. With ShapeWriter, unless it recognizes a proper name, in which case it uses the appropriate capitalization automatically, words you enter are treated as lower case; there is a "change case" key that cycles the word you just entered between initial-cap, all-caps, and lower case. You can change the case of individual letters in the middle of a word, but it requires moving the cursor to the point immediately following the letter you want to change and then hitting the "change case" key. This mostly works okay in running text, but it's completely useless when entering a password in the browser, for instance, when the text is replaced by all asterisks.
3) It is incompatible with some applications, notably the "Word to Go" word processor in the DataViz "Documents to Go" package. In particular, hitting the Enter key inserts an underscore character instead of ending a paragraph, and there are some other issues with backspacing.
4) Some ASCII characters (notably _ and ~) are hard to find and enter, and some ([ and ]) just aren't there are all. Most accented alphabetic characters are there but hard to enter (requiring an extra-long keypress to bring up a sub-menu from which to select).
The good points about ShapeWriter are the price (it was free, the last I checked, although I'm sure that won't last forever) and the way it handles automatic capitalization, automatic spacing, and recognition of the single-character words "I" and "a" (ordinarily tapping a letter after tracing a word adds that letter to the preceding word with no space, while those two need a space and, in the case of "I", need to be capitalized). It's very rare, in my experience, for the current version of ShapeWriter to make mistakes in those areas (previous versions had bugs, so if you last tried it a few weeks ago and encountered errors in this area, that's probably why your experience differs from mine).
SlideIT, on the other hand, does not suffer from those problems. It has a real Shift key that works just as one would expect, it works fine with Word to Go, and it's somewhat more forgiving of minor inaccuracies in tracing. It also has a very extensive set of Unicode characters that are pretty straightforward to enter. In addition:
1) It has a macro-expansion capability -- you can add abbreviations that will show up in the list of possible words a shape you've traced might be, and when you select the abbreviation from the list the corresponding expanded text will be inserted. (For example, you might add your initials as shorthand for your full name; if you trace your initials and pick that abbreviation from the list of suggestions, your full name will be entered instead.)
2) It has prediction capability: type or trace the first few letters of a long word and the full word will appear in the list of possibilities.
The main disadvantage of SlideIT is its price. It currently goes for €5.99, or a little over $8.00 at current exchange rates. I would probably use SlideIT over ShapeWriter except that I really don't want to pay $8.00+ for something that, in my opinion and for my usage, is only a little bit better than what I already have for free. Different people have different needs and desires, of course, and SlideIT may well be worth $8.00 for many.
(You should be aware that the "SlideIT Lite" in the market is not really a free version; instead, it's a time-limited demo version that expires after a few days, refusing to enter any more text until you buy the full version.)
