I've read through these both, but I can't decided which would be the adventure to start my group off with. I was just wondering if you all had any opinions on the story quality and how the well tuned the challenge was for new characters and overall just which one you all thought was better. Thanks.

Trouble Brewing is longer and has less of a backstory if your players have strong identities for their characters and group. Under a Black Sun is good and your group could probably clear the whole thing in a single session if they didn't take every optional encounter.

Trouble Brewing by it's completion either has the group in contact with a mid/low level ranking Hutt giving them the chance to climb up the ranks of underworld power, or it underlines the treachery and corruption of the Imperial government.

Under the Black does, at it's end, put the group at odds with the most powerful criminal organization in the galaxy so that could be a strong campaign arc.

If you're happy/good at adding your own links between content you could do both, starting with Trouble Brewing, if they take the Hutt option to return the bounty then have him (instead of the Pykes) be the one that has the issue with Leechos ("You've been so good with this bounty, I have another for you. I need to know the identity of a Bounty Hunter who attacked one of my shipments"), then create/play out the part where they break in and slice the Black Sun base. After that you can play Under a Black Sun as is.

The alternative is to start with Under a Black Sun and have the Pykes tell the PCs to bring the Bounty Hunter to Formos for delivery. Have the Pykes demand that the PCs still owe them some cash ("where is the missing spice?") and they want it quickly, then use the Cantina scene, plus play up the bounty on Bandin Dobah to draw the PCs in. You could create a link between Leechos and Dobah as Leechos sold some of the spice to Dobah cheaply (before trying to sell the rest of it to Black Sun) as Formos was close to the location of the hijack. Alternatively play the Droid scene as written if the group is heroic or there is anyone who would be interested in standing up for droids or wants to recruit the R4 droid as a companion.