Texas
The state of Kentucky has the longest border, being north of Tennessee, which is much longer east-to-west than north-to-south.
The state with the longest east-west distance in the contiguous United States is California. It covers a vast area from the Pacific Ocean to the Nevada border, making it the longest state to traverse.
In the west, the state of Montana has the longest linear border with Canada. In the east, the state of Michigan has the longest border, including the Great Lakes.
No, Tennessee is not the longest state in the U.S. While it is a long state, stretching about 440 miles from east to west, it is not the longest. The title for the longest state belongs to Alaska, which is significantly larger in both land area and length. Other states, like Texas, also have considerable lengths but do not surpass Alaska.
I am assuming by east to west coast you mean the Contiguous US, or the Lower 48. In which case Texas would be the largest state.
Width (longest distance, east to west): 357 miles
Asia stretches the longest from east to west. From one side to the other, it stretches over 7000km.
Mexico has the longest east-west coast in Middle America, spanning approximately 2,200 miles along the Pacific Ocean.
Hawaii is the widest state east to west.
Interstates I - 10 (the longest), I-40 and I-80 run east -west across the US.
The State To the west of Colorado is Utah. The state to the east of Nevada is also Utah.