Royal,
I use the Palmone own brand screen protectors on my T5. I've not tried any other products because the Palmone protectors work fine, so I can't say how they compare.
I have seen comments from other users that they can decrease the screen's sensitivity and thereby make graffiti more difficult to use but I've never found this to be the case. One of the advantages of the Palmone product is that you get a nifty plastic applicator, rather like a credit card) which makes it really easy to prevent air bubbles getting trapped underneath the protector (very irritating!).
the one thing I cannot emphasize strongly enough is DO get a screen protector and soon. Replacing a scratched screen protector costs cents; a dollar or two at most. Replacing the screen on your Palm will be very expensive and they DO get scratched.