The answer depends on the quantity of questions, if you have an indefinite number of questions, you can use "algunas", but if you have a few questions, you can use "unas". You can use "Las" with other characteristic like "las siguientes" and it concerns to the next.

In my opinion "algunas" is the best choise... "unas" poorly used on that context... and for sure "las" is not used on that context.

¿Cuál artículo? ¿Como escribir correctamente? These sentences are correct and can means the same "Tengo algunas preguntas" (The most clear)