I believe top tier in any airline or hotel program, with the possible exception of UA 1K (largely because of the systemwide upgrades) is overrated by most. Then again, it really depends on your desires and travel patterns.

If earning maximum points/miles is your thing, then getting Hilton Diamond is a step up over HHonors Gold as the Diamond bonus is 50%. At Starwood, Gold & Platinum both earn 3 pts/$ so there is no difference. Diamond also alleviates the onerous Hilton capacity controls....not an issue at Starwood.

If you can only get top level in one of these programs and mid-tier in the other, it seems to me you are better off with Hilton Diamond (top) and Starwood Gold (mid-tier). You give up no point earning potential at Starwood and increase it at Hilton.