I personally prefer the Hawksaw. You sacrifice some stability due to it's higher fire rate but that only makes it better for staggering snipers. It wrecks against hand cannons because they cannot reliably land shots on you. I've been at the receiving end of a Hawksaw many times while using my beloved Eyasluna and it was not fun. Now the PDX isn't bad, it's certainly better at longer ranges but I want something that'll stagger enemies in medium ranges and melt people in closer ones. I want to give hand cannon and auto rifle users a run for their money in closer ranges and the Hawksaw does that perfectly. But this is simply my own preference. More people probably have the PDX and I blame that for it's lead in the poll but then again, the Hawksaw is 150 legendary marks or a random drop from legendaries so I understand.

Most people with say pdx because it's the one they have

Both of them are really good. I have a full auto high stability pdx which is amazing but the vendor hawksaw is great. I'd recommend the vendor version as it has an amazing roll.