I have not personally taken aikido. I have taken it's parent art (the art that some/most moves were taken from to form it's own unique style) aikijiujitsu. I have studied a lot about it because I am interested in possibly taking it soom also. Anyway...
I think aikido can work for someone who wants to defend yourself. It is highly debated on the internet and among martial arts how effective it is for self-defense. Some people will tell you it is absolute garbage and a waste time (so they recommend some other martial art to take instead) and some will tell you it is very good. Which opinion is right? They all are. For some it is garbage and for some it is very good (it depends on the makeup of the person taking it). Here is the basic way a self-defense situation will go down with aikido: A guy has some problem with the aikido guy. The aikido guy avoids getting into a fistfight with the guy (aikido's philosophy is one of peace and harmony. A true aikido guy will not get into a fistfight and avoid it until last resort). The aikido guy tries to talk his way out of it and remain a healthy distance from the potential attacker. The attacker continues his threats and moves aggressively toward the aikido guy. He grabs the aikido guy and the aikido guy responds by twisting the guy and throwing him to the ground (the aikido guy make use some strike to loosen him up for the throw). On the ground the aikido guy will put the attacker in a pin (an aikido pin puts the attacker on their face with one of their arms outstretched and controlled by the aikido guy). In the pin the aikido guy can talk the other guy down or break his arm (whatever the situation needs). This is the basic strategy of aikido. It is avoid conflict, remain defensive, if attacked then throw them to the ground and then put them in a pin. If this sounds good to you then aikido may be for you. It is often said about aikido it takes a long time to learn how to do all of that against a real attack. I would agree. I have heard opinions from different aikido people of being able to throw/pin attacker would take from 1yr. to 4 yrs. It all depends on you how good you are and how much you practice. I would say probably 3 years. I couldn't do a throw with a pin with 2 years of aikijiujitsu. I would say it would have to take another year. It is a martial art that is good for people that are not into slugging it out with someone (like most martial arts focus on). It is all about staying in your aikido shell and avoiding an attack until they attack and aikido must be used to defend. An interesting quote I read in an aikdo book made a good point about aikido. It was said from people who took judo about aikido. They said to never attack an aikido person or you will defintely be thrown. It is a good comment about how if you stay defensive (in your aikido shell) and don't attack, your chances of getting an aikido throw can be good. Aikido does have it's drawback and that is why a lot of people here have already suggested to you to take some other martial art instead. It is not good with striking (it has some simple strikes to help loosen some one up for a throw but that's about it), the throws are a bit complicated to learn, it lacks a lot of groundfighting skills, it doesn't provide good sparing or competition (where you can learn to do these skills agains someone trying to resist you), it doesn't demand you to get in good physical condition, doesn't deal with kicks, and so on. This is the reason a lot of people say take another martial art instead. But, as I said, those are the people that say it is garbage. The others that say it is very good would say more: strikes are not important in aikido or for it to be effective in defense, the throws can be learned and used from faithfull practive and hard work, groundfighting can be avoided or can be dealt with by creative use of aikido principles and techniques, sparring and competition are not necessary to use aikido (they actually interfere with aikido's noncompetitive nature), being in good condition depends on how much you want to get in shape on your own, dealing with kicks can be down with creative use of aikido principles and techniques, and so on...What is true? It depends on you and how you see it. It is somewhere between the garbage and very good in my opinion. It would take a lot of devotion and faithful practice for it to work for you. If getting attacked can happen anytime very soon for you I might not recommend it (like if you are in high school). I would recommend mma, brazillian jiujitsu, boxing, etc. instead. If it is not that immediate of a concern then aikido may be a decent choice for you. It has it's goods and bads but all martial arts do.