I would go with ones that have liquid droppers...the ones with test strips or powders haven't been as reliable in my opinion...but I think it comes down to what you like to use and what your budget is. I just have the one brand that all of the places carry (Petsmart, Walmart, LFS)...don't even remember what it is, but it seems to be giving reliable results and they are easy to use so I would reccomend them. I can look at the brand when I get home...or maybe someone else knows which ones I'm talking about.