They have same number of abilities. MRD can equip 10 cross-class but WAR can equip 5 (limited classes to pull from, only GLD and PGL) and 5 warrior-only abilities. Personally, as a WAR, I only equip warrior's soulstone when I do dungeons since warrior's abilities seem more suited for tanking. Soloing or FATE I still prefer MRD. That changes a bit at 50. You can still wear darklight, darksteel and allagan as Marauder but you cannot wear AF and AF+1 unless you're a warrior. Relic weapon and its +1 also is job specific so your strongest weapon for MRD would be the Axe of Crags which is a random drop from Titan HM untill you get Allagan battleaxe.