The most common spelling is the EA. There are about 150 commonly used words that use it, ranging from bean and beat and beach to disease and treacle.
Almost as common is the EE spelling. There are about 130 commonly used words that use it, ranging from beech to squeeze and steeple.
Obviously, many of these spelling variations are there to prevent confusion in writing, if not in speaking. Examples include flee and flea, beet and beat, meet and meat. These distinctions seem logical and there is really no big problem.
But there are a number of words that don’t bother to use either the EE or the EA to get the sound. They spell the sound with a single E. For example, we have words like decent, hero, relay, he, she, we, me, secret, and cathedral. And there are some that use the silent E: these, sphere, and mere.
As for words that end with the EE sound, there are hundreds of them, and they generally form three groups. The largest group is words that end in Y, like baby and robbery. Many of these words end in LY and are often adverbs, such as actively and brightly. A smaller group contains words that end in EY like chimney, jockey, and money. There seems to be no reason for the E in the EY spelling. Compare rally and valley, turkey and murky.
Then there are about thirty words that use IE for the EE sound. They range from believe and diesel to priest and goalie. And there are a dozen that use the EI spelling: ceiling, deceive, and seize.
Let us not forget that some words use an I to get that EE sound. These are often exotic imports like ski, debris, ravioli, macaroni, tsunami, khaki, and bikini.
Finally, we have to have a few really strange spellings like quay and people.