There are many cryptocurrency which are in top category. You can not gauge a particular coin as top 6 coin for the investment. I think there are many which are included in top150 according to the marketcap will be considered as top for the investment. Among these i think the recent blooming are  CAPP, Datum, SwissBorg, PundiX, BTT, and KickToken can be regarded as top6 as for the investment.