There are advantages and disadvantages the CRJ-200 and the EMB-145 have over each other. These advantages/disadvantages are based on my experiences in both airplanes.

A CRJ, more often than not, can carry a full load of passengers with an alternate filed when some models of the EMB-145 can't. The EMB-145 EP is especially bad. If an alternate is filed, 50 passengers isn't happening on that airplane.

The EMB-145s have a lower fuel burn over the CRJ-200 in most cases. They have a lower MGTW and also have engines with lower rated thrust.

From a passenger perspective, it's a toss-up. The CRJ does have 2-2 seating as opposed to 1-2 seating in the EMB. The CRJ has better overhead capacity with bins on both sides of the cabin. A big plus for the EMB is recirculation fans where the CRJ doesn't have any.

If I'm making fleet decisions for an airline, I take the CRJ-200 over the EMB-145 with fuel prices remaining where they are. The first consideration is getting passengers to their destination safely and both airplanes can do that. The CRJ-200 gets more passengers to the destination when scheduled than the 145s I have experience with.

When discussing the CRJ-700/900 vs. the EMB-170/175, I can't comment because I have no operational experience with the 170/175. I can see passengers preferring the 170/175 over the CRJ-700/900 due to the larger cabin.