If you can only RD one of them and you plan to visit both on the same day, my choice would be to RD HS, park hop to AK, and return to HS for the later evening hours.
HS has a lot of headliner attractions that get long wait times by mid-morning, which stay long throughout the day and may lighten up in the last 2-3 hours at the park. RD at HS may enable you to get in 2-3 attractions before the wait times grow insane. Around 10-10:30 am, several shows begin, so if wait times for your preferred rides become ridiculous, you can still enjoy a couple good shows before park hopping. Arriving at 2 pm to HS, it's hard to accomplish much until the evening.
By contrast, AK's wait times often get a lot shorter by the time you'd park hop, as it seems that more people park hop away from AK than to AK. So, when parking hopping to AK in the afternoon, check the wait times and do anything with a reasonable wait, including one of the shows. Watch for opportunities to get in a short line. If you're going at a time of year when it gets dark fairly early, stay just until dusk to see Pandora glowing after dark. It's stunningly beautiful. Then, assuming HS is staying open later, return to HS to take advantage of shorter wait times in the last 2-3 hours of the evening.
If you plan to buy ILL$ for Flight of Passage and/or Rise of the Resistance, that would ensure you get to do both of those with a short wait.
Genie+ is quite helpful in HS, especially if you're not going during a relatively quieter time at the parks. With G+, you could get in more headliners at HS, including stacking some for the evening. You could also G+ Kilimanjaro Safari and Nav'i River at AK.