The dyes with the most intense signals that IDT offers are the Alexa Fluor and ATTO dye classes of fluorescent dyes. Signal intensity is not effected by position within the oligo sequence. Green, yellow, and some orange dyes can be partially quenched by guanine bases. Therefore, if you decide to order a dye in that range, you should try not to position the dye immediately next to a guanine base. Read more details
about this quenching effect.