Use the pipe, all other conditions being equal.

Whether hollow or solid, the larger the diameter, the
better off you are for that antenna. It is not a
thickness issue. A solid 15 mm vs a hollow 15mm diameter
offers no advantage, RF wise. But in a 15mm diameter versus
a 3mm diameter comparison, the 15mm wins every time.

Assuming you shorten the elements and you want to sacrifice (small) gain
for bandwidth !!!

WB5UOI