A diplexer will do what you want with minimal insertion loss, probably less than .25dB. A two way splitter will have at least 3dB loss and usually more, plus you can have all kinds of weird interactions between the antennas where they overlap.
I have a Diamond brand diplexer that does 1.3 to 460MHz on one port and 840 to 1400MHz on the other. I can test it to see how low the 840 side actually goes and I know you can tweak them internally somewhat to move the bands around.
prcguy