comparing a pure ranger and a swashbuckler is kinda hard. Rangers get more hit points (d10. swashbuckler, d8). The ranger can specialize in any weapon, swash can only specialize in thief weaponry. Since the Swash does not fall under the warrior catagorization, he/she does not get the bonus THAC0 that a ranger would. Swash DOES get a bonus in THAC0 and damage every five levels however. but that is not nearly as much as a ranger. BUT, of course, the swashbuckler has all the thieving skills, except backstab which sucks, but if the swashbuckler did have that, it would be unfair. So, after saying all that i have to agree with Aurican. It all depends on how you wanna play. It's Role-playing, thats what makes it fun.
so play whowever suits your style the best!
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Wise man once said, don't spill beer on cHiCkEn HeD