Best pump for water hauling?

Hello all. I have been doing a lot of reading here and now I'm looking for some advice. I am looking to buy a truck to lease on hauling salt water. I have been doing it as a company driver almost 1yr. My question is what pump to buy? We have challenger pumps on most of our trucks.

Are there better options for vac tankers? Would I be better off going with something that runs off a wet kit or stay pto shaft driven?

 

Well I have literally looked at every water truck I come across at the disposals and 99% are challenger pumps and most(75%) are shaft driven. I personally would prefer a trailer mounted unit myself.

I have used a cowboy/pony pump before and was not a fan.

Been looking at pumps all week and I have ran across a few used units for less then 1/2 the price of new. Would it be worth the gamble if I could get one for $2500 instead of $6500? I know challenger sells rebuild kits for around $700. My only issue with the ones I have seen for sale is they aren't still hooked up and I can't see them run at time of purchase and they are being sold as-is.