I prefer the styling of the Extrema Ratio... The handle seems grippier and more swelled, which will feel better. The ER sheath seems better with no hard surface outside to make noises, and the optional pommel length really makes this something special, while the Spartan looks like any regular dagger with a regular kydex sheath.
You will find over time boring styling can make these things more tiresome to own...
The narrower blade profile will definitely defeat ballistic vests better, if that's any use...
Don't be worried about the extra-pointy tip: It can still be strong, and fine points tip-slash better than broader points. Not that the Spartan point is broad: It is not a relative advantage between these two, just a general observation...
Because of the full tang, both are slightly overweight at 9 and 10 ounces: In that size range a dagger should be 7-8 ounces: Weight is the biggest advantage of daggers, when carried in a shoulder harness.
My favourite "practical" daggers are all long discontinued items, but can be found on Ebay: The best sharpness out of the box is on mint Gerber Guardian IIs, with a weight of 8 ounces, outstanding zero edges and 6.75" blades: Still cheaper than those: Don't be fooled by the Gerber name, this is old Gerber...
I like Seki-City models like the SOG Desert Dagger, because the Kraton handles are nice and light, but Seki-City is not zero edged so not as sharp as Gerber: Even the super-impressive Al Mar Shadow IV, best designed dagger of all time imho, 7.75" blade on 9 ounces, is very dull and needs a trip to the professional sharpener to compare to a Gerber Guardian II's zero edge...
I also love the Blackjack 8.50" blade Tartan Dirk, but only for lashing as a spear point...
My absolute favourite is cheap but extremely hard to get, and again not sharp like the Guardian II: The Junglee Waterloo: 6.8 ounces for a 6.9" blade (!!!): Unbeatable, with nice serrations, but like all Seki City daggers not that sharp. Very poor unsecure sheath, so that is big minus. The Kraton Handle is outstanding.
What to avoid is custom daggers: Smooth slippery handles, often full tangs, so heavy and slippery, the very opposite of what a dagger should be: This is one area where factory beats customs any day.
Gaston