The advantage of a destroyer as a salvage ship is that they are small, fast and have 8 highs.

In the area of destroyers, the best for cargo capacity is the Gallente catalyst that has the most cargo capacity when fitted with expanded cargo holds. The Amarrian coercer has more lows, but less cargo to begin with so that even with four lows it still doesn't have the hold capacity of the catalyst.

Being classified as a small ship lets you use small rigs. The small salvage tackle can be found for under 1M isk each while a medium tackle is about a 4M investment each.

Battlecruisers can do a very good job as a salvage ship having lots of highs and lows. Though the investment on making a salvage tackle battlecruiser means putting down 30M for a ship and another 12M for rigs that you will only be using for salvaging can be a bit of a turn off for some.

A not too odd ship to see salvaging is the Exequror. While it doesn't have the highs that a battlecruiser would have, it does have significant cargo space making it much easier to clean up an L4 mission (the loot off of battleships can take up some space). It is also a ship that one may have laying around after graduating from low end cruisers to other ships and don't feel bad about making it a light hauler/salvager only.

It really comes down to what do you want to invest in a salvage ship.

Destroyers, especially with salvage tackle rigs, are very good at this job.

A lot of people use a hurricane.

Something like this is pretty good

[Hurricane, Salvager]
Expanded Cargohold II
Expanded Cargohold II
Expanded Cargohold II
Expanded Cargohold II
Expanded Cargohold II
Expanded Cargohold II

10MN MicroWarpdrive I
Large Capacitor Battery II
Large Capacitor Battery II
Large Capacitor Battery II

Small Tractor Beam I
Small Tractor Beam I
Small Tractor Beam I
Small Tractor Beam I
Small Tractor Beam I
Salvager I
Salvager I
Salvager I

Medium Salvage Tackle I
Medium Salvage Tackle I
Medium Salvage Tackle I