Sealing wood countertops needs to begin with a question. How do you plan to use your countertop? Some wood countertops are used as food prep areas where actual chopping is done. This is usually referred to as butcher block. It is perfect for this use and proven over hundreds of years. The best sealers for these tops are mineral oil or butcher block wax. Butcher block was is just mineral oil, food grade mineral spirits and beeswax. These products keep the wood healthy but are not sealers. Water and other liquids will be able to penetrate so they are not good choice for kitchen countertops with sinks.
Most kitchen countertops are used for multiple purposes but not direct chopping. For these tops our standard sealer is a satin 2K polyurethane. It's an extremely durable form of wood sealer producing a water proof seal that is highly resistant to most all household liquids including bleach. It can be cleaned using any common all-purpose cleaner like 409 or Windex. It's also a maintenance free sealer never needing re-sealed. An ideal finish for busy family and commercial kitchens.