Unfortunately for you, Ed Robinson's only does their Lanai charter on Wednesdays, and you mentioned above that you're planning for a "weekend". That's going to narrow you down to one choice if you insist on diving only with one operator for both Molokini and Lanai, and that's Lahaina Divers, which goes to Molokini on Saturday and Lanai on Sunday.
We dive with LD quite often as we love their big 46' Newton boats (motion sickness issues for me), and we've found the crew to be fun and professional. However, the trade off is the potential for up to 24 divers on the boat, which frankly, we've only experienced on their afternoon charters because of the Discover Scuba folks.
Be aware that the boat ride to Molokini is LONG from Lahaina. Typical profiles are 65' for 35ish minutes. We dive with computers so usually get 45 minutes on both dives, but they will send hoovers up to the boat early. LD also does 2 dives at Molokini crater, where some ops only do one there and one off-shore of Maui on their way back to the marina.
I'd really recommend that you book with an operator out of Kihei for Molokini and one out of Lahaina for Lanai. Extended Horizons (12 pack, same dive profiles as LD) and Lahaina Divers are your choices out of Lahaina. (Many prefer EH to LD for Lanai, but I hate being crammed onto EH's boat). Out of Kihei, go with B&B, Mike Severns, or Ed Robinsons to Molokini...all are recommended highly.
Also, bear in mind that mid-March is the beginning of "spring break" season, so book early to make sure you get the charters and operator you want.