Liquid test kits are generally more accurate than test strips. As for brands, many of us here use API and find them reliable. I am told that Sierra's are scientifically better, but also considerably more expensive and not so readily available. API kits are available in many stores.
As for what you need, initially (new tanks) it is good to have tests for ammonia, nitrite, nitrate and pH. Once the tank is established, periodical tests for nitrates and pH are advisable. The API master kit contains these 4 essential tests and will be less expensive than buying them individually. Once the tank is running for a couple years, replacing the pH and nitrate kit alone works well; having said that though, it is useful to have ammonia/nitrite kits handy. The regents in test kits only last so long, most a couple years, some less (depending upon the test), so replacement is necessary.
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