Of that list, DeCastro hands down would be the pick. He's probably a top 10 guy on most big boards and won't get out of the top 15 though so I'm going to pretend he's not an option.
I know Hill is everyones draft crush but I'm unsure the value is there. I know everyone is clamoring for a tall speedy guy, but I'm unsure if we need a tall speedy guy as a starter and as a high draft pick. I don't think Hill fits Harbaugh's offense as a #1 or #2, as I doubt he'll have one of his two starting receivers running vertical routes almost exclusively. A guy with Hill's skill set seems to be a better fit as a backup in this offense. Someone who can rotate in to provide a vertical threat. I think Harbaugh and Baalke would rather draft a guy more willing to go across the middle to make tough catches and provide explosiveness after the catch (and hopefully Crabtree also will reach his potential in this area) as opposed to making big plays specifically through the air. That's why I think our ideal fit at WR is Kendall Wright. He's a bit small but has never had injury concerns and has an innate knack for finding seams in the defense to create big plays on any route, not just a fly or deep post.
Glenn seems like an ideal fit at RG for us, a mountain with quick feet who would fit our man blocking/pull heavy scheme. But he wouldn't be a fit at C and if the Niners are convinced Kilgore is a long term answer (which they may very well be), then he probably would get bumped down the list a little bit. Then again, Davis hasn't cemented his status as the franchise RT though he has vastly improved, and Glenn could also provide value as a potential RT.
The reasons to draft Fleener are well documented and I don't want to beat a dead horse. On the other hand, the team clearly values and likes Delanie and he seems accepting of his role as the #2 and Vernon and him have a good relationship, I don't think an extension is too unlikely. I know this is contrary to widespread belief on this site but I'm also unsure he's truly a value pick at #30. He's clearly the #1 TE, but that doesn't necessarily make him a round 1 guy. He very well could be, I won't pretend to be a professional scout, but I think the sudden surge of importance and value at the position in addition to his status as the #1 at the position is causing people to overvalue him on talent alone.
Of this list, ultimately I'd say the pick is Konz. He's a Wisconsin guy - a college known for pumping out technically sound lineman - and he plays a position where smarts and technique matter more than anywhere else on the line. He can compete at RG right away. Hell he can probably compete at C right away, I don't know what kind of investment we have monetarily in Goodwin but I remember his contract being rather modest. Either way, he can upgrade the line right now, but more importantly lock down a position of need for many years in the future.