I started out as a Titan, and loved the tanking aspect... but you won't be able to select Defender subclass until lv15. Even as a tank, I was still viable in Crucible; just watch out for other classes as some of them can 'burst' your bubble. I'm really looking forward to the new Titan subclass in the next expansion. I might just make it my main again. On the other hand, I also love my Warlock. The Voidwalker subclass is especially handy towards a specific exotic weapon bounty (you'll encounter that later). In any case, let me know if you need help with anything. Hopefully you'll find the one that best suits your playstyle.