Considering singles only, it has to be Maleeva - she has a handful of Tier I and Tier II titles, is one of a few players who has won titles on all surfaces, and has a highest ranking of No. 4.
While we can't really include Dokic in this group, due to her age, I'd say she has been more successful than the rest other than Maleeva. She has a couple of Tier I titles, has made a Grand Slam semi, won titles on clay, hard, grass and carpet, and has a highest ranking of No. 4.
Sugiyama has 2 Tier II and 4 Tier III titles; Testud only has one Tier II and two Tier IV titles. Farina Elia has three Tier III titles, all at Strasbourg and has never been in the Top 10 (highest at No. 11)
However, when you include doubles, then Sugiyama clearly has had the best career out of this group - 28 doubles titles, including 3 slams, and one US Open mixed title to the six singles titles, a top 10 singles ranking and a No. 1 doubles ranking.