Ryley has access to the Stasis Rifle, Repulsion Cannon and his PRAWN can withstand greater depth pressure. Also he survived the planet despite being infected by the Kharaa so lorewise he was under a time pressure to reach his goals.
In a 1v1 Riley would win be cause of better weaponry and such, but I think Al-an would just flat out destroy Riley if he hurt Robin (especially if it was a fight to the death)
I guess it depends on the situation. If they just get into a fight and Al-an is around then Riley will lose, if both have their "standard weaponry" then Riley would win, if just a mostly unarmed 1v1 then it could go either way.
