I have played both, and both are strong with ToB.
Blades: They can use two exploits very efficiently. The
Melf's Minute Meteors Dual-Wield Exploit and the
Mislead Exploit. Both exploits are covered in detail in this thread.
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Swashbucklers: They have better base AC and THACO than the Blades, but remember that Blades can have magical assistance( Blur, Stoneskin, Improved Haste, etc...). In ToB, Swashbucklers can have Whirlwinds.
Both: In ToB, the differences starts to blur, because they nearly share the same pool of special abilities. Blades may not have access to Whirlwinds, but the MMM_DW Exploit gives them 6 attacks per round, and it is a range attack.
Blades can play it safe and use the Mislead Exploit to get undispellable invisibility( used very effectively to pulp Bodhi and the rest of her gang).
Swashbucklers can also play it safe and use traps to ambush the enemy( but in ToB, Blades get traps too).
The only real advantage that Swashbucklers have over the Blades, is that they can Lockpick and Detect/Disarm Traps.
Blades will have more Hp than Swashbucklers, thanks to Find Familiar.
Both are soloable material( with ToB installed).