I have SPYDERCO Military and I have inspected Al Mar SERE 2000 some times at different blade shows. They are so different knives that it is really hard for me to put them into the same category.
Which one is better for hard use? This depends on what you consider as hard use. Being present here (BFC) for some time I have noticed that speaking about hard use folks pretty frequently have in mind tasks a knife is not intended for, for ex. prying, pounding, loading folder blades in closing direction etc. In another words
hard use quite frequently is mixed with
improper use.
Another case of
hard use term abuse (sorry for pun) is speaking in masked form about typical knife fight situations.
Well, SERE with narrow ground blade shaped more like the dagger one (although sharpened on the single side only) would make good choice if your are going to fight using pure stabbing techniques. Very secure and comfortable handle would serve this purpose as well. And it is very, but really very! strong knife to do not say overbuilt one. Pretty much onto heavy side for daily carry although not too big as long as it stays in your pocket. Definitely it is not the best cutter, even using slashing techniques in knife fight there are a lot of knives what would perform better.
Important: SERE has the pocket clip set up for tip-up carry what I cant consider as any good combination with liner lock because it doesnt hold closed position too firmly.
Military with fully flat ground blade and thin edge is excellent cutter, more than likely it could cut circles around SERE. It makes pretty big although very slim and lightweight package housing unmatched cutting power. On the other hand thin tip makes it certainly not the best choice for stabbing. The handle is oriented more to prevent palm sliding backwards on heavy cutting too. Also handle construction with single steel liner and short plastic backspacer is far not as strong and stiff as SERE one. The clip is positioned for tip-down carry.
So the answer on your question depends on what you need your knife for. Since Im not going to stab anyone (or to go into any knife fight at all, using whatever fighting techniques), do not like to carry more weight than I really need and do not feel myself safe and comfortable with liner locks carried in tip-up position I do not have SERE at all.
On the other hand Military is my favorite tactical-kitchen folder. Way too big to carry it in publics in urban environment but just right for around household and outdoors carry. It sticks out of my home jeans right rear pocket for more than 3 years and so far is not going to be retired.
Does the Military come with double metal liners, like on the AFCK?
Dennis is quite right, Military has single-sided steel liner nested into G-10 scale.
Oppps, edited: I didnt notice your question original formulation which is stronger and not which is better. SERE is way stronger with no doubts.