What these guys have said already is right. (well not Gregor's 'subtle' mocking of the Tau
) I really would suggest you pick up a Tau battleforce as it's one of the few battleforces available that contains an entire legal army (your minimum requirements are 1HQ and 2Troops) most dont have a HQ included, though the Space Marines and their Chaotic counterparts can have a HQ created/converted from the all the bits in the battlefield box.
If theres a GW/gaming club near you i'd recommend visiting and seeing if you can borrow one of the store's small armies to play a game, see if you actually like the way Tau play and if they suit your playing style.
Playing Styles can vary so much that its important to get the army that suits you rather than try to force yourself to play an army that you dont find a laugh to battle with. I personally play Space Marines because im a terrible general but Marines are forgiving enough to look past that (as long as your opponent isn't a fearsome veteran) though SM dont generally excell in any one area without having to except a number of disadvantages.
Tau on the other hand are the closest thing in 40K to modern warfare (i know IG would seem like the ideal example but stay with me). They operate in squads rather than huge platoons, they emphasise rapid response and combined arms rather than static firing lines (theres more but i just saw the clock and it was my bed time
3hrs ago). I've generalised and rambled but i hope i've been some help.