At heart I'm an Audio Technica guy. So let me start out by telling you that Audio Technica and Audix are my two favorite brands of pro audio microphones. As far as Audix is concerned there are plenty of reasons to invest your hard earned money into an Audix microphone. First reason is that I have rarely found any microphone brand that can deliver as much gain before feedback as an Audix microphone. This applies to vocal handheld mics like the Audix OM5, and also to the instrument microphones such as the I-5.
The importance of having a high resistance to feedback can not be overstated. Feedback is the enemy and the number one question we get at Direct Pro Audio is how can I combat feedback. Feedback, and how severe it is depends on a large number of conditions, but let us take a moment to remember a cardinal rule in pro audio: "It all starts at the mic". There are several tools that can help you control feedback. These tools include feedback eliminators, equalizers that pinpoint feedback frequencies, compressors, and microphone channel strips. All of these tools can help, but they are all secondary devices designed to deal with a problem created by using a bad microphone for your intended purpose, or for poor microphone placement, or for a lack of proper gain-staging.
My suggestion is to nip the problem in the bud. For instance, let us say that you need incredible amounts of stage volume from your monitors because all of your musicians are deaf. Well, why don't we just solve the problem by using the correct microphone for the type of setting we find ourselves in? If you need the ultimate in gain before feedback, the Audix OM7 is the one and only choice to go with. The only issue is that you need quality microphone preamps in your mixer to work properly with this microphone. You see, the Audix OM7 is not very sensitive, it is purposefully designed that way to give you maximum gain before feedback. To make up for the lack of sensitivity, you need to really gas the gain knob on your mixer to compensate for this. It works like a charm, but a good preamp in a quality pro audio mixer is the key to this working out well for you.
Another favorite of mine is the Audix OM5. The OM5 compares favorably with the Shure Beta 58A or the Sennheiser E835. All three of these mics have low handling noise, and fantastic off-axis rejection. Here again, I give a slight edge to the Audix microphone. The OM5 just sounds a little more life-like, and as a bonus, it is made in America, so you are supporting jobs right here in the USA.
Let me close by saying this. If you are very experienced in running sound, you can rock a gig with the crappiest microphone on the planet. I have seen it done, I have done it myself. Nothing tests your mixing abilities more than walking into a venue only to find Optimus and Radio Shack microphones. It makes life tough, but it can be done. But most of us in pro audio are weekend warriors, and the best advice I can give you is to go with the right microphone for the right purpose.