Any divination lot system is based on the idea that the lots represent a piece of the cosmic system. Once one realizes this, it should be evident that the question is more of a question of "how well do we understand the Celtic as opposed to the Germanic cosmology." As someone who has been somewhat involved in both the Celtic reconstructionist and Germanic reconstructionist movements, I guess I am probably somewhat qualified to take a stab here...
I think everone on this forum (so far) seems to speak English, which is a Germanic language. The cosmological model manifests partly in language, so it is often easier to see the model of a group when you speak a related language. English is a direct decendant of the Migration-Age Germanic tongue that was used when the Elder Futhark was in use. On the other hand, I think that to really understand the Ogham, one would have to learn (at a minimum) Gaelic, or preferably Old Irish fluently enough to be able to read, write, and speak it properly. The Old Irish-derived languages (all three forms of Gaelic) are relatively difficult languages to learn because the concepts of space and individuation are different. For example:
We say "I am hungry" and they say "There is hunger on me."
We say "I went to see the doctor yesterday" and they say "The doctor was at me yesterday."
We say "He is a musician" and they say "There is music at him."
We say "I love so-and-so" and they say "My love is on so-and-so"
and so forth.
Also the above examples are of course translated back from Gaelic literally. The syntax is radically different from English as well. Like the Latin-based languages, you have adjectives following nouns, but the word order of the senence is different altogether. While most Indo-European languages are Subject-Verb-Object (i.e. "Joe (subject) went (verb) home (object)") the Gaelic languages are Verb-Subject-Object. Furthermore, you have no pronouns, so your prepositions are conjucated. Hence instead of the first sentence in Genesis I, we get something that looks like: "In-it the beginning, created-him God the heavens and earth." At about this point I gave up on learning Gaelic fluently :-(
The second issue is the question of the extent to which the Celtic mythic cosmology is really well studied compared to the Germanic cosmology. In general, the Germanic studies have a bit of an advantage here in that there is a bit more written on the subject that is readily available to English-speakers. However, in both cases, I believe there are enough works available to help get one to the point of understanding the concepts of sacred space and time that are used as the basis for the divinatory endeavor. If you only own one book in this area, let it be "Celtic Heritage" by Alwyn and Brinley Reese (sp?).
The third issue is how well the Ogham as a specific system within this framework is understood. I personally think that this is one area where there is still a lot of work to be done and our understanding of what the Ogham represent is still developing. We do know that they were clearly a cypher of sorts (and possibly inspired by the Germanic "hidden staves" traditions). Note that Tree Ogham is only one form of Ogham-- you have King Ogham, Castle Ogham, Hog Ogham, and a large number of othersystems superimposed upon eachother. There have been some important works in this area within the last decade or so (particularly "A Guide to Ogham" by MacMannus) which have yet to be well absorbed into the popular material.
In the end, I think that Ogham for English-speakers is a more difficult path to follow. However, in the end it is the path, not the tool, that counts. The question should not be "which is better" but rather "which culture do you want to spend your life learning more about?"
