Hey there Miller, please forgive me for what probably seems like nitpicking, but for us to answer you most effectively and for you to understand in turn, try to limit the use of subjective language in your posts as much as possible. What I mean by this is, try your best to remember to avoid terminology like "best, like, euphoria, good, bad etc". I'm sure I don't have to tell you that people perceive the world differently on a general basis and if we are to examine this thread specifically, "best" could mean, what provides the most analgesia, longest duration of effect, most intoxication and so on, just to name a few.
If you're trying to ask how to maximize the effectiveness of what you have, Methadone is pretty straightforward. Compared to Opioids like Heroin and/or Morphine, there is not a significant degree of difference between bioavalability and route of administration. Basically, an injected dosage of Methadone might be 15% stronger than an oral dose, at most, with significantly more risk involved.
Case in point, Methadone is best taken orally for most any purpose, be it analgesia, Opioid maintenance, detox etc.