I gotta side with Stu on this one. More shares = more dividends therefore it is better to get more bang for your buck (more shares per BTC to maximize dividends paid) at the cheaper exchange.

If you are truly long on ActM then you must agree with the above.  If you aren't in it for the dividends then you are a price speculator.

Also, your argument that cheaper shares still equal the same number of bitcoins, that is true only until the price changes.  If you own 15% more shares and the price moves up X on both exchanges then you make 1.15*X on Bitfunder versus BTCT.

So your only argument left is liquidity risk, and somebody has already pointed out that trade volumes are virtually identical on both exchanges.  Plus there are more total shares listed on BitFunder so technically it would have more liquidity.