Well, it's kind of a toss up. Time Crisis, as a well known series, is definitely a mainstream title. Do I like it? Meh. Time Crisis (original) on a 50" monitor, yes. TC2...It's okay. Would I want one in my game room? Commercially to make money, yes. At home, not so much. TC3 or 4....graphically, nice game, but not my choice personally. For me, the gameplay is...well, lacking something.
L.A. Machine guns, by comparison, I've only played on the 50" version. It has a certain feel to it that I like. Again, personally, I would put it in either game room, commercially or at home. It does make money on the road, and I like it. I generally don't care for Sega pieces (as a whole), but I like this offering. It has enought on-screen action going that there really isn't a "pattern" that I can see. So as a result of that, it tends to keep the gameplay original and exciting. Plus sound-wise it keeps the blood pumping, the whole package together is a very-well made game IMO.
Don't take this as a L.A.Machine guns is better than TC thread...Time Crisis is a very well-recieved game on the commercial market, and you'll get a lot of positive comments from folks coming to your home and seeing a TC machine there. I just have seen it too often in my experience (every place I ever worked in the arcade industry had a TC of some kind, it wears on you), and I've gotten burned out from it. Crisis Zone is also a good piece, if you have that option. Technically, part of the Time Crisis series, but different enough to be a step away from it as well. If it were me personally and it was a 50" L.A.M., I'd go for it, but it's really your opinion overall...Play both first, if you can and then decide for yourself.