Terran is usually the best choice because they are well rounded and can have the highest population, meaning you'll get the most out of the 100%+ allegiance for tax income, especially if you go full social spec, in which case the tax income can get pretty crazy when the population hits max.
If you're planning to use it more actively as part of your economy/war machine though it'd probably be best to go with a desert planet since they are easier to defend and get more logistics slots.
I would hesitate to recommend an Oceanic as they are harder to defend than the other two although if you're playing against AI this may not matter anyway. Like Goa said if there doesn't seem to be one of those nearest your biggest resource producers, just go with something fairly central, since the Allegiance bonus to all your other planets is going to matter more in the end than the tax income from the one planet.