Vacon is a Finnish company that was founded by ex-ABB engineers. But the X series drives come from a product line they bought in the US from TB Woods. So the X line drives are the old TB Woods E-Trac drives, they are very good, very rugged, very reliable even if they are a little long in the tooth as a drive line goes now. Other Vacon drives from the Finnish group were sold here in the US for a long time as the Cutler Hammer SVX9000 series, until the exclusivity clause expired a few years ago.
The ACS-310 is decent entry level drive for ABB, should work fine for pump applications. I like ABB's programming interface, I think its one of the easiest to program.
Ive used them both, either would be fine in my opinion. Sorry, that probably doesn't help.