Another Option...
Declare @t1 Table(mid int, val varchar(100))
Insert into @t1
Select 1,'123' union all
Select 2,'123456' union all
Select 3,'123456789' union all
Select 4,'123456789123'
Declare @vChk varchar(100)
Set @vChk = '123'
Select Top 1 * from @t1
where val like '%' + @vChk + '%'
Order By Len(val) desc