Water major then Defense makes a pretty solid explore combo. (likely my favorite) Water enlivens can boost both dodge forms and damage resist forms and if you end up with an offensive water form the enliven will boost it too. The last water enliven will allow you to take your defense major form under water for exploring a ton of areas that most people can't. This combo enables you to explore a wider variety of areas than any other shifter build, in my opinion, but can be hampering because there is a good chance of only having defense forms for land fights, and that causes a lot of strategic thinking about where to lead mobs to water or swamp if you have a strong water form that isn't amphib.

Defense and defense can make a decent explore team too. You have more chances at getting a regeneration form than any other major/minor choice which can be handy in many situations. This isn't as important after the changes a few years back that greatly slow regeneration during bleeding, poisoning, through protections, etc, but top tier regeneration forms are still very useful for hit/run tactics on a lot of big mobs. The drawback is that you have very little offense capability when solo, so it'll usually take a long time to kill high level mobs.

Defense then Utility is a good combo too because defense enlivens can boost dodge, evasion, and damage reduction, making big impacts on the way different forms feel and react. Utility was explained some time ago as 75% offense, 75% defense which means they're pretty good at dealing damage and can make long fights feel more managable, especially if paired with defense forms. They too have a high chance of landing regeneration forms, although not as adept as defense ones.

Defense then Offense is superior for exploring than Offense then Defense but both are workable. I find that the added boost from defense enlivens in most situations trump the various boosts to damage from offense enlivens but will give special notice to "unstable mutation" which allows a shifter to do damage to some mobs that may be immune to their normal attacks.

Utility first is a decent balanced combo for (1) defense and (2) water because they allow you to cover some annoyances. One enliven slows mana burn, one covers saves, etc. And you have a chance at air and amphib forms with utility. These combos don't excell at anything but can be very versatile if the right forms are landed.