Test Strips are EXTREMELY UNRELIABLE. Test Strips read for Nitrogen in the Water vs actually measuring the Nitrates/Nitrites.
Now this could be a huge debate. I personally use Red Sea, for everything. I find them to be reliable and easy.
The top brands are (in no order):
Seachem, Salifert, Hannah Checkers, Red Sea, Elos. I know I'm missing one I just can't think of it.