Personally, I find the 60 seconds of Soul Trap spell a bit overkill, but I can respect it because you need to get pretty close to cast it (I can't seem to see any effect when casting it anywhere farther than 3 feet)

My assassination dagger and bow both has a 1 second Soul Trap on 'em. Primarily because I can slit the opponent's throat, but also because I don't play with any "lingering" effect, so anything beyond the moment I hit the opponent is pretty much useless.

It makes an incredibly durable enchantment. I enchanted 'em with Grand Soul for crap and giggles, and I can't seem to bring the meter down even for just a notch

How about you?

Halidir's soul trap, infinite I think but very costly on the soul gem front. Made a Headsman's Axe with it and Ebony Blade leech and I can only get about ten ish hits out of it before needing a recharge. Luckily a petty soul gem will fill it though and I did create it a while back when I had a much lower enchanting skill, should really make one now that I am about 100 skill to see if it is any better.

1 second soul trap on my melee weapons and bows. If I need to conserve charges I can always whack the enemy around till they are almost dead with something else.

I had a 10 secons enchantment on my greatsword in my 1st char, good enough

This !

3-5 secs just to be on the safe side

As above. Bow's I enchant for longer to account for poison.

I rarely bother with longer than 3 seconds or so...though 60 seconds has interesting implications...illusionist hits enemy with Fury, shoots an arrow into target, and sits back while target's buddies kill it and Poof...soul gem goodness!

3 Seconds, to account for thing's like Followers or random NPCs getting the killing blow on my target.

Usually three seconds. I tend to use a weapon which captures souls exclusively until I have a reasonable number of gems, then swap to a weapon which does elemental damage. Whe I start running short of full gems, it's back to plan A. Never keen on the "hit-with-soul-trap-weapon-swap-to-other-weapon" way of dealing with it.

2 Seconds. It would be 1 second but there are times when a follower or NPC gets the final blow in.

5 seconds.

But since I pretty much one shot everything anyway...

3-4 seconds on bows and 1-2 on blades or maces. Good point about the poison on the bow taking a bit longer.

3 seconds on one-handed, 5 on two-handed.