There are a variety of series of Latin texts on the market for high school level instruction, many of them vastly dissimilar. Some are suited to one style of teaching, others to a particular kind of student; each has its strengths and weaknesses. I am familiar with Jenney's, Latin for Americans, Ecce Romani and The Oxford Latin Course. I have been taught out of Ecce Romani and Latin for Americans; the rest I have used in independent study. My analyses of these texts comes from both personal experience and conversations with teachers who I know through the JCL.
Proceeding in alphabetical order:
Originally published in a five book series of paperbacks, Ecce's strength lies in its focus on reading comprehension and translation; though its focus on Latin Grammar is blurry at best, students learn to translate intuitively rather than mechanically, which leads to wider vocabularies with somewhat lesser accuracy. The storyline of the text follows the life and times of a fictional Roman family during the Pax Romana, lending the series its other major strength--any student educated from Ecce will come away with a knowledge of Private Antiquities superior to that developed without devoted study of any other text, that is, the Private Antiquities are worked so elegantly into the texts that ipso facto of translation the student is familiarized with aspects of life and culture which are jostled into insets and special chapters in all the other texts I've seen. However, Ecce fails to develop any kind of compositional skills, putting parochial students learning Latin for service in the Church at a disadvantage. Another complaint which I have heard from teachers is that the Latin used in the early Ecce texts is highly artificial, little more than English sentences translated into Latin--id est, the student fails to pick up on Latin idiom with the facility of other, more strenuously accurate texts.
Jenney was most certainly an instructor after my own heart; I keep one of his first year texts at hand because it is an excellent (and nearly complete) overview of Latin grammar condensed into a year's curriculum. The prime advantage of Jenney's older texts (The new version has been broken up into more easily-digestible, colorful versions--That is, what originally comprised Jenney's First Year Latin is now First and Second year, to a total of four books covering half the information of the original four) is that the assiduous freshman will, by the end of his first year of high school, be able to read and compose in Classical Latin with greater facility than offered by any other course. The great misfortune, however, is that the American education system is too flabby to actually follow that curriculum. I have heard from every teacher I've praised Jenney's to that what Jenney expects to be accomplished in one year is the work of three unless one weeds out all but the brightest students and works them to exhaustion. Another complaint about Jenney's, even the modern edition, is that his translation exercizes are extremely short; this puts the teacher of a large class at a disadvantage, because only a fraction of students may be called on to translate sentences in class. Similarly, the translations are pandemically uninteresting, and I must admit that the coursework is too strenuous for the average student in the American system of educating the masses.
Latin for Americans
Another text that follows the life of a Roman family, LFA does so only for two books, the first and second year, after which the student knows all the necessary rudiments of Latin grammar and is launched into the realities of Latin prose in the third and final book. The most versatile of the bunch, LFA has both lengthy, challenging translations and a competent overview of grammar, providing the best of both worlds as achievable in the high school setting. Whereas Jenney's is best suited for a private academy or otherwise academically advanced setting, LFA works equally well in either public or private school systems. (Ecce Romani, it seems to me, is best suited for less advanced classes in public education and unsuitable for the bulk of talented students.) LFA is well balanced in introducing Private Antiquities subjects; similarly, it is the only series that places the student in 'Real Latin' in the third year as opposed to the fourth, with the exception of the antiquated Jenney'ses no longer in print. In my opinion, LFA is the best-all-around series of those reviewed here.
The Oxford Latin Course
Hands down, the Oxford Course will produce students far superior to any other in terms of translation, surpassing Ecce Romani because of the superiority of both its translations and the presentation of their requisite grammar. Though the presentation of grammar isn't as strenuous as LFA's, it is concise and about as unthreatening as it is possible to make Latin grammar. Although the Oxford Course initially follows stories regarding Horace's boyhood, it is soon to push the student into two to three page long translations of the highest instructional quality I have ever seen in a textbook. These translations sparkle with prose style and authenticity, while being of such a length that the student ceases to translate what he reads into English--rather, he reads the Latin language in a way no other series elicits. However, the series has several instructional disadvantages: firstly, it is only published in softcover, which means the texts must be replaced every year--every two at the maximum--to remain legible and presentable. The second unfortunate flaw in the Oxford Course is that its attention to private antiquities is cursory at best, focusing more on mythology within its translations than on any working knowledge of Roman culture. However, used in conjunction with another text (How glorious it would be were Jenney and the authors of The Oxford Latin Course to collaborate), the translations of this series provide enrichment for students of any skill level.
One series worth mentioning, though I have never been exposed to it in person, is the Henle Latin series, compiled by a Jesuit priest; I have heard many good things about the series, particularly for its efficacy in instructing parochial students. Henle's is the only series that I have heard of which makes an explicit focus on Latin composition as opposed to simple reading comprehension, teaching grammar for construction rather than deduction.
In terms of overall instructional value for all students, I would rank these texts:
1. Latin for Americans
2. The Oxford Latin Course
3. Jenney's Latin, and
4. Ecce Romani.