if you really cant do both, i'd go for the run because the time spent running is usually longer than the swim, so you can get better at the run and save more time than if you got better at swimming. Get in some speedwork and slowly increase your mileage and you'll become a better runner over time. Still, remember that you cant focus ONLY on running (even though i feel it is more important than swimming). I would personally recommend balancing your training on a 3:1 ratio btw running and swimming. If you go through 4 days and run 3 of them, make sure you swim AT LEAST 1 day also.

You'll definately get the biggest time gains from the run since it's a longer leg of the race, and with some dedicated, focused training, the times can drop fast pretty easily.

However, if you're really not comfortable with your swimming ability...then swimming will be better for your piece of mind and comfort level going into a race.

If you feel like you can swim a long time, just slowly...I'd say go with the run.
If you feel like you barely survive the 300m swim...go with the swim

+1 Yep, no questions asked. Also if you get all kinds of beaten up in the swim finish that bike and run will be a real chore, but if you limp through the run your done after it's over. I'd go with the swim.

I would go for the swim, mostly from a safety standpoint. I think every swimmer attempting an open water triathlon should feel strong and confident in the water. For me, that's the bottom line just for basic safety. After that, working on speed, etc. is great.

Running is much easier to improve on your own. Swimming, it's much harder to do without a good coach. Swimming is just much more technique-based. At your current swim pace, I'd say that a coach could really help you swim stronger and faster.

I say swim. For a first timer (as I was this year) the swim was the biggest hurdle. Having confidence going into the swim is a big key to conquering the HIM for the first time if you aren't a veteran swimmer b/c how you start your race physically/mentally is important. DNF on the swim was my biggest fear going into my HIM.

Its easier to train yourself on the run. Running more will, generally, make you a better runner. Swimming more doesn't always make you a better swimmer, it can just solidify bad habits. Self coaching the swim for 6 months before you get a coach can make it that much harder to learn proper technique.

Assume you can only do one program, and for comparison purposes, let's assume you will make a 10% improvement in whichever one you choose (ie, either your run pace is 10% faster or your swim pace is 10% faster). At this point, which area of improvement will result in the biggest time savings should be obvious:

Given your current stats, you have a 100m pace of 2:23. If you swim 1.2 miles at this pace, you will finish in ~:46. If you join the masters group and manage a 10% improvement, that means you would finish in 41:30 (2:09 pace), for a time savings of ~4:30. Not bad at all.

If you run the half marathon at your current pace (5k in about :30 or 9:30 per mile), you will finish in 2:06. If you join the marathon training group and make a 10% improvement, you will drop roughly a minute off of your pace (8:39) and finish in 1:53, for a time savings of :13 minutes.

So, assuming a 10% improvement in one event but not the other, which 10% improvement translates to a better time savings? The run.

I agree with all the points, but I think the main question would be: Are you wanting to just finish this HIM? or, do you want to kick some butt and have a faster time?

If you just want to finish, definitely concentrate on the swim (it'll pay off more in the long run). Since you'll receive some nice form coaching at the beginning of your learning, just as others mentioned.

If you want to have a faster time, you'll definitely do so by concentrating on the run, just as TriSooner calculated.

Being new to the Tri sport, it may also be very beneficial to get comfortable in the water. There are a lot of stories on this forum that mention people getting freaked out when they do their first open water swim (especially due to the massive loads of people but also due to limited visibility). Being more comfortable in the water will allow you to have a much easier adjustment to the OWS.

wow I love the internet ....thanks for all the input but I'm doing the master swimming. I do not want a DNF..nor do I want to drown... I think I will benefit more from swim instruction. My first tri in Feb has a 300m swim and last year sub 3 min was the tops, wowowowowow howhowhowhwohow. I must be missing something. i need/will learn>>>Next dumb Q in the next week