I use side-based Initiative in my DF game. We used Partial Surprise rolls to determine which side goes first, and then all of that side (PCs, or NPCs) goes first. A substantial victory can mean surprise, otherwise, we're just seeing who got started a little quicker. We changed the Partial Surprise rules a little because "win and go first, lose and be stunned, tie and you're tied" thing is pretty brutal - most fights start with even a prepared group being pummeled for a while before they react.
But Christopher Rice put up an interesting post about random rolling to determine place in the initiative order. It's a one-time roll, of course, since GURPS doesn't have combat rounds and thus gets weird quickly with re-ordered initiative (take it from someone who tried that, back in the day, before anyone bothered with Wait.)
One idea that springboards off of one of Christopher's ideas is this:
Initiative and Surprise are determined randomly.
The leader of each side makes an initiative roll per Partial Surprise, p. B393. Add the result to the highest Speed of any character on that side. The side with the higher total goes first.
As Side Based, but add the leader's roll to each inidividual's Speed. Arrange turn order based on that number. Optionally, everyone rolls individually, and takes the bonuses from their leader.
This basically means a side with smarter characters, guys with higher Tactics, a leader (especially with Born War Leader!) will generally go faster. They may even pace the fight against fast foes who aren't as well lead. A leader with Tactics, Born War Leader 2, and Combat Reflexes will be rolling 1d+5, 1d+6 against less-intelligent creatures (and they'll roll 1d-2 for being leaderless, 1d-1 if one has Combat Reflexes.) Very fast opponents can still go more quickly, but it'll be very uncommon. Very tactically organized foes will be a surprising threat.
Just a thought. I haven't tried it, but it does merge the Partial Surprise rolls and rules about the benefits of organization, leadership, Tactics, etc. with a Speed-based random-roll based initiative system.
I should post my Partial Surprise house rules at some point, too!