My sister and I are looking to do a DNA test to aid in our genealogy research. What is best practice here? Would one of us provide better results or will they be the same?
You should consider testing both of you. Because each sibling has it's own DNA.
You can increase chances of finding matches if you buy tests in different competitive labs. For example, you can test in FTDNA, and your sibling in 23andMe. In such a case you will be able to use databases of matches of both labs. And you can upload your and your sibling's raw autosomal data to free GEDMATCH service and prove your relationship there. Or there is another way to put data into one database: use import feature of FTDNA. It consumes data from 23andMe, puts it's data into FTDNA database and make it avaivable for matching.
If you have male and female siblings, it is good idea to start from male siblings, because male persons have more types DNA (atDNA, mtDNA, Y-DNA) than female (only atDNA+mtDNA). But in any case you should consider testing of all your siblings.
IF you don't have any older-generation relatives who can be tested, and IF you can only do ONE test, then bear in mind that a male autosomal test includes 22 pairs of chromosomes plus one X, while a female autosomal test includes 22 pairs plus 2 X's, so you get a few per cent more matchable DNA with the female sample.
On the other hand, if a male gets a significant match on the X chromosome, you know with certainty that it's on the maternal side, whereas with a female sample you can't tell from the X match alone. As with the previous example, the likelihood of this being a factor is fairly small, but it can make a difference.