Crusader all the way, if possible coordinate with at least one more player on your team and try and build in some synergy as Axel mentioned.
The two most obvious possibilities I can think of involve 2+ crusaders.
Iron guard's glare is absolutely amazing in low magic settings, especially with more than 1 crusader around. (Enemies you threaten get -4 to hit your ally), with Phalanx fighting and making a shield wall you could make yourself virtually unhittable at lvl 1.
Scale mail (4)
Heavy Shield + Shield wall (5)
Iron Guard's Glare (4)
AC at lvl 1: 23 (enough to make most CR1 monsters require a 20 to hit you, and quite a few CR2 monsters would have a very hard time hitting you as well)
Another, slightly more offensive version would be to use a polearm/spiked chain (I hate the spike chain, though for a "gladiator" I can see it as flavorful). Using this you could each give each other +4 AC, and all your allies could have +8AC (against melee attacks at least) =D
Combine that with the extra durability the recovery strikes (Crusader strike for example) give you, and you should have an incredibly potent team starting at level 1. At higher levels it gets even nastier with stuff like thicket of blades, tactical strike, shield block, and white raven tactics(!!!). Having more than one person on your team with white raven tactics is absolutely devastating, especially considering the crusader's method of recovery, you don't need to be shy about using it, as you are likely to re-acquire it within a few rounds.