I dislike Sta-Set X too. Gets kinky, it's stiff, performance isn't all it should be, etc.
3/8 may be small on your hand - I like a little more meat on my halyards just for the handling of them, but that's personal preference.
My C-30 did indeed have 3/8" halyards. I found them small.
3/8 is fine.... depending on your budget.... almost every chandlery online will have a strength chart for the various lines. The keyword for your halyard search is "performance double braid"... All the rope manufacturers will offer choices in that category. Choose the one that fits your budget, and or course, fits the winch, cleat and blocks that'll be used to control them. That said, for a cruising sailboat, good quality double braid polyester, such as Samson XLS, will certainly work, but check the strength chart to make sure it's in your comfort level. BTW, I've never had a problem with 3/8" halyards, especially if you wear gloves. You don't handle the halyard near as much as the sheets anyway. I know Dave sells rope products here on SBO... but I'm going to provide this link to show you how easy it is to learn about running rigging. Have fun. Selecting Line for Running Rigging | West Marine Choosing Running Rigging | Sailing World
I use Yale ULS and its antecedent, UULS. Very soft on the outside, seems to be very kink-free, with lower stretch stats than Sta-Set/Sta-Set X. I am not a fan of NER at all - my longtime preference has always been Sampson XLS (new version: XLS3, available at Defender, Fisheries Supply, Vela, and a couple of others - check stock before getting your hopes up).
Awkward but true: the only reason so many people use NER at all is because Big Blue sells it (actually used to own it) and it's all they know. Ironically I bought all my Yale UULS from a West Marine (where I was manager) that was closing; it had been a BoatUS store and district management would not move the old stock to the new superstore if it wasn't still something WM would carry. I think I paid 0.08/ft for +/-350 ft of 3/8" (wicked laugh boowahahahahahahahahahahaha).