I've stuck to the lines which have kept me in awe (thank goodness i dont like all of the series). My constraints are:

1) Classics - just because they pay homage to the G1 combined with modern engineering (i cant buy G1 because they're too expensive to complete).

2) Masterpiece

3) animated (i didnt really like the look of the toys, but i liked the story and the fact that the toys look exactly as they're portrayed in the cartoons).

4) selected customs and other lines where the toys have resemblance to the above lines.

5) budget (and my partner).