I want to get rid of the default classes and add my own to the fields. I was always using field.tpl.php but i've read some tutorials where people are doing this with Display Suite. So should i do this via field.tpl.php or Display suite?
It's matter of opinion, really. I'm using DS and it works fine, but it might have disadvantages later on, because I will have to export my settings to code with Features.
Also, DS isn't your only option - you can also try:
and others. Which depends on your other needs - for example, are you planning to use DS multiple display modes handling?