Tuning snare drums of a modern day drumline is a very subjective topic. In fact, the sound of the groups I've worked with over the years has evolved from year to year. Some of this has to do with the sound we're trying to achieve for a particular repertoire. Some of it is just personal preference.
I always recommend drum heads by REMO. They've been the industry standard for decades, they sound great, and they're amazingly durable.
For the batter (top) head, I like the sound of the WhiteMax or BlackMax heads. These two models are very similar, but the white adhesive in the WhiteMax can tend to give it a slightly brighter sound. These days, kevlar heads are pretty standard for drumlines, and I like that the "max" series offers a little more "give" than some other choices, which feels better to play on.
For the snare side (bottom) head, I really like the sound of the Falams II Smooth White. In my opinion, the snare side head has the most influence on the overall sound of the snareline, so we like to get these really tight. Because of this, the Falams (made of thin kevlar) seem to hold their pitch better than mylar and tend to last longer. In a perfect scenario, I like the bottom head to be higher in pitch than the top head. Tuning the bottom head to a high D-natural seems to be a good sweet spot. This is pretty high though, so don't crank up the snare side head so quickly that it doesn't have a chance to settle into that tension. Blown bottoms can get expensive so this is an area where you have to take special care.
Tuning snare guts is also an important part of a well-rounded snareline sound. This aspect of tuning is often neglected, but really does affect the sound. There are different schools of thought, but I've always preferred for all the snare guts to be tuned identically. Tuning snare guts can be tedious, and can take some practice to become good at it. The more you do it, the easier it gets. Plus, the more you do it, the less "out" their tuning will become as well.
Another thing to take into consideration is the size of your snareline. How many players are there? I've adjudicated marching band shows all over the world, and it always amazes me to hear a 2-, or 3-person snareline with kevlar heads cranked to the stratosphere! Perspective is important here, folks. My recommendations above are what I've found (and the good folks I've worked with) works well for a 7-10 person snareline at the drum corps level. This is probably not the best strategy for a younger, smaller snareline in most smaller marching bands. Cranked kevlar doesn't blend with an ensemble very well if it's a small snareline, or if the players aren't ultra refined. In smaller ensembles, or with less experienced players, I strongly recommend using mylar heads such as the Powerstroke 77 (top) and Clear Snare Side mylar on the bottom. They're more forgiving for the players and will generally blend with a band much better.