I think that the result you have achieved with the tiles you were given is fairly good. The main thing you need to improve on is what's going on behind the tile and your fixing technique. Given that you say you're slow, it clearly matters to you that you do a nice job so I'm sure that any advice you've had here will be taken in.
Going back to your orginal question, don't bother with wooden battens if you're having to work with poor quality tiles. Use spirit levels or buy some aluminium battens from Trade Tiler and cut to length. These will give you the best start but you'll probably still need to use wedges too.