(almost) Always raise rents to keep up with the market, otherwise your property will be have a property $200 below market rents in a few years with no way of raising them on the current resident. I great way to make this not a big deal is to let people moving in know that rents will probably go up a little bit to keep up with the market as well as costs such as taxes and insurance going up. Usually what makes people mad about rents going up is being surprised by it.
Another good thing to do is give them options. Give them a year option at a $20 increase a 6 month option at $40 increase and a MTM lease at a $75 increase.
I often send a letter telling people their options and if they don't want any of them I tell them to give me a call. I usually ask for a little more than I am willing to accept so that if they say the rent price is going up to much I have an amount I am happy to lower it down to. For example if I want a $15 increase I may ask for $25 and then negotiate down to $15 if they think $25 is too much but if they are happy with $25 then they will just sign the lease at the higher amount. This tactic needs to be treated with care as you can get yourself in trouble if you do it wrong.