When it comes to answering the question of what the best concrete sealer is, its hard to pin point one type of sealer for all applications. There are a lot of factors that go into choosing a sealer including application (driveway, patio, etc.), substrate (concrete, brick, masonry) and functionality (salt repellent, waterpoofer, oil repellent, decorative).
Below is a quick reference guide that highlights common applications, substrates and functionalities:
Concrete Driveway: If you are looking for deicing salt protection use a silane/siloxane blended sealer. If you are looking for oil and staining protection use a silane/siloxane with a stain protector like the Siloxa-Tek 8505.
Concrete Basement: If you have active moisture or water issues it is best to use a two step application by first using a densifying primer of a lithium silicate carrier, followed by a penetrating silane/siloxane product. If you do not have active moisture issues and are looking to proactively seal, use this fantastic all-in-one product found at homedepot.com
Concrete Blocks/Cinderblocks: Because of the porous nature of the concrete cinderblocks it is best to apply three to four coats of a penetrating silane/siloxane sealer.
Stone/Stucco/Slate/Bricks: Stone, stucco, slate and bricks are best protected using a penetrating, natural finish silane/siloxane sealer that will not encapsulate the substrate so it is still able to breathe.
Patio/Pavers/Pool Deck: When sealing a patio, pavers or pool deck it is best to first figure out the desired finish if you are looking for a natural/clear finish, low sheen or wet look/gloss. If you are sealing a salt water pool a silane/siloxane blend is going to be the best option to keep the pool deck from spalling and pitting. Keep in mind that the natural finish products are penetrating and give the longest lasting, best protection. Whereas low sheen and gloss finishes typically need to be reapplied on a more frequent basis.
Natural/Clear Finish: Penetrating silane/siloxane sealer
Low Sheen: Water based acrylic
Wet Look/Gloss: Solvent based acrylic
Waterproofing/Salt Protection: A penetrating silane/siloxane like this one that gets great reviews from HomeDepot.com
Oil/Staining Protection: Lowes.com offers this product in a concentrate so you get to control the mixing and application. It’s great to protect driveways from oil stains and leaf staining and backyard patios from BBQ grill and food stains.