Kakashi has more working for him then Gaara's ultimate defense.In terms of a more well rounded shinobi in skills Kakashi has this.Gaara has his ultimate sand defense and his sand based jutsu.
I'm not saying that's nothing, in fact it's a hell of a lot.Few people can get in close to him, few can actually penitrate his armour, and his attacks are brutal and powerful...
but that's the only thing he has. I haven't seen him throw a punch, or defend against a genjutsu or anything.Kakashi is the strongest shringan user, for somebody outside the actual Uchiha clan. Nobody (IMO) who had the chance to weild a Sharingan would ever compare to him.With that unique eye he has copied and mastered over a 1000 jutsu.Now with the few we've seen, we've seen powerful offense (of all ranges short-long), defense.Not all 1000 of his techniques are elemental based so we could expect more.We've seen his high level of taijutsu, and know that he atleast has some ability in genjutsu (Only seen once,we haven't seen him cast as a method of fighting in a battle or ever been in a situation where he had to repell except with Itachi's Tsukuyomi, which couldn't have been broken by his own means for reasons of him not actually possessing the Uchiha blood).
On the issue of Kakashi vs. Gaara. Kakashi has more field expereince in battle
(fought in a war when he was a child and was in the Anbu for a period), and he's
been shown to be one of the more brillient strategists in the series.
He's fast (although we don't know if he's fast enough to get to Gaara) and he's resourceful.
I see Kakashi's more rounded abilities, and stratigics out playing Gaara.