I have always avoided Tuvalu coins like the plague.  The Cook Islands as well.  There are enough Australian coins to waste your money on.

My father taught me that the only pennies to use for two up are Bald Edward English pennies (1901-1910) as these were used during WW1 by the soldiers.  They evidently believed that they were the best balanced pennies, but I guess that this is debatable.

I did get some funny looks years ago when I went to a dealer in London and asked for his worst examples, as I was going to polish one side and paint the other black!