Yeah the IS looks to be the weakest of the bunch because of its smaller size, and its less-sporty nature. But personally, unless the G25 is much better equipped, I'd have a tough time overlooking the 323i and C250 in favor of the G25. No matter what people say, Infiniti is no BMW or M-B.
In what respects would you expect the BMW and Mercedes to be superior to the G - comparing base models, of course? I don't know that I'd be willing to grant them presumptive superiority on nameplate alone. While I haven't driven the current C-class, I have driven past models and came away rather underwhelmed. Take away the impressive hood ornament and there wasn't much that made a strong positive impression. Good? Yes, absolutley. But there are plenty of good cars on the road today. The 335i is an awesome machine and just about definitive of what a sports sedan should be. But the 323 is not the same beast in terms of engine or suspension.
I think the G would prove close enough to either of those to make it a game.
Jaeger
PS - Canuck - you think the G should be 34k?? Seriously??
Matter of personal opinion. I'm amazed every time I drive my in-laws 12 year old C230 with almost 200k on the clock, still solid as a rock to this day. I can only imagine how great owning/driving a brand new C250 would be with the small V6 instead of a their 2.3L I4. As for the 323i, its base engine still is a gem IMO. I've driven one a few years ago (when it made about 190hp) and it was incredibly smooth.
I might be wrong, but I still view Infiniti a notch below those two (and Lexus) in terms of overall refinement. Their horrible interiors from 7-8 years ago are still very fresh in my mind, where there were plenty of hard plastics to be found that creaked as soon as you put a finger on them. That's probably changed since, but that's still tainting my opinion of them after all those years. But of course, I'd drive everything in the price-range before buying anything to make sure I'm not wrong here, but to be honest, I'd be surprised if the G25 came out as the winner for my $.
For the G37 though, I might be ready to overlook a bit more considering its value proposition compared to its competitors... but at a similar price, I don't see the G25 being worth it against the big boys.