I have two powerheads available to me to replace the stock pump in my 29gal biocube seahorse tank. Should i use the 160 GPH or the 145 GPH? Im guessing either one would do but im not sure what the advantages to each end of the 5-7 turnover rate range would be besides better flow and aeration.

when the flow rates are than close its kind of a toss...
what brands are they (that you are choosing between)

And what are their watts... the higher the hotter.

And what are their watts... the higher the hotter.
yes, thats a great point.. in these smaller tanks you have to be aware of heat generation

both are penguin brand, i dont know the wattage off the top of my head but im guessing go with whichever has the lower wattage?

yeppers...lower watts = less heat, which is the number one problem with the "plug-n-plays"