To be completely honest, why not just try using both? Just carry a sword and a pair of daggers and try each out on your own to see what you like more.
Also, if you end up liking the dagger and bow combination, try going Ranger next. Although you do end up losing a couple of handy skills with the daggers (Masterful Kill and Invisibility), you can gain a couple good bow skills (especially Tenfold Flurry, which is a beast at most ranges).
The one thing I never liked about the Assassin vocation is the augments... they have some good buffs, but they're all conditional (mostly only active at night). Ranger at least has some good tricks, such as increasing the range of light when using a lantern (makes night or cave travel a bit easier).
I personally use Swords for fun/general mobs. and switch to Daggers for single-target showdowns/bossing.
Swords: Setting traps under dragons and various mobs with Powder Blast + Intimate ___ (forgot) to take out almost any human-sized monster.
Dagger: Gale Harness+Hundred Kisses=Win over any boss. ...ANY. Then third skill to whatever I like, really.
PS: To any who didn't know, Gale Harness increases movement speed and attack speed. What you might not have known ? It also increases bow attack speed. Fivefold Flurry+Gale Harness = As good as a Ranger's Tenfold shot. :D
This. You'll want to use both. If for no other reason than its more skills you can keep equipped to handle a variety of situations.
I use sword most of the time, but keep my Daggers on hand for dealing with big monsters. Not only is Hundred Kisses great for that purpose, you'll also be able to double jump, which makes getting up those monsters much easier.
That leaves sword free for the fun stuff. Yes you could use Gouge for Big Monster killing, and its arguably better than Hundred Kisses. But Kisses is useful on any target, and Gouge is a wasted slot when you're not fighting Big Monsters.
Likewise you'll want to eventually use both Shield and Bow. Its just more skills you can easilly swap to on the fly without having to visit the Inn.
Sword will in general work fine for most things but if you are really looking to take down large monsters quickly then dagger/shield is the way to go. Showdown from your shield lowers defense and raises strength. Combine that with gale harness and it gets a bit ridiculous. Really, unless you love swords, just carry a dagger, shield, and bow with you at all times.