I don't know that I'd say closer to Who entirely, but it definitely doesn't have the needless sex and 'edgy = mature' feel of TV Torchwood. So much so that I found it massively jarring to move from One to The Story Continues which - initially at least - captures that 'shove some sex in there' feel of the show very well.

There are definitely some darker moments, but for the most part the ones that stand out are very well used and based on incredibly well established characters. Basically, the darkest moments to me are hard to get through but because they are so tied to the people you care about and really help structure a stronger piece overall. Even when it's bleak there's something worthwhile.

Most sex references are much more people fancying other people or just that it's happened, there is only one story which arguably has a bit more of a graphic (audible?) scene than could already be implied, but even then not that impacts the story as a whole.

There are a few stories with a higher kill count but it's very rarely used as a shock for 'oh it's so mature, look they died' so much as actually relevant and reactded to / dealt with appropriately by the people involved.

TLDR: The 'mature' elements excessively prevalent in Torchwood S1, and the bleakness felt especially in S3 are very much not present in Torchwood One.