choiceで変な文字を入力させない、が正解だとは思うけど利用可能なドライブから選択させた方がスマートじゃない？
@echo off
for /f "tokens=1-27 delims=:\ " %%@ in ('fsutil fsinfo drives') do set "drv=%%A%%B%%C%%D%%E%%F%%G%%H%%I%%J%%K%%L%%M%%N%%O%%P%%Q%%R%%S%%T%%U%%V%%W%%X%%Y%%Z"
call set "drv=%%drv:%SystemDrive::=%=%%"
if "%drv%"=="" echo ERROR: No available drives found.&echo Check the target drive connection.&pause &exit /b 1
set /p <nul=ドライブを選択 [%drv%]:
for /f %%a in ('choice /c %drv% /n') do set drv=%%a:
echo %drv%
pause