Okay sorry forgot to share my intended purpose for this camera. Basically gonna use the kit lens for general purpose shooting, then get a 50/1.8 for portraiture, and lastly something which stretches to 300mm for outdoor sports photography.
Looking at both of your points, it's really hard to make a decision. They both are very value for money cameras though, and it's such a close fight despite their different merits.
Well, I have absolute respect for Pentax, their compact lenses, their excellent optics.. and the Pentax K30 looks really cool, especially with the different colours. If you are going to shoot outdoor sports, the full-weather seal is going to be very useful.
However, I think there is one word consumers shd always keep in mind:
Relevance, and in this case, Relevance of the features
to your requirements. K30 is already one up, with the full-weather seal, A57 cannot beat that, you simply can't shoot with the A57 shelterless in a thunderstorm...
..if you are going to do that...
But since bro pinholecamera has listed the strengths of the K30, it is only fair we list out the strengths of the A57:
a) For general shooting, the A57's articulated LCD is going to be useful for those awkward angle shots, especially when you do those overhead shots (CNY lao yu sheng, concert with lots of people crowding around you, etc), or ahem... ground level shots... (eg. baby crawling on the ground, dogs running in the park, and other shots that will not get you into trouble with the law
). With the K30, you just gonna be trying your luck in lots of your shots. Or be kneeling down or standing on a stool..
b) A57's 12 fps shooting vs K30's 6 fps shooting : If you are going to be doing outdoor sports photography, well, if you need to zua, you need to zua, cuz athletes/cars move really fast, so the A57 is going to offer you twice as many frames as the K30 to get your motion shots.. unless you are shooting old men playing chinese chess in the park. Anyway, jokes aside, you can check out
bro Rashkae's F1 shots, not too bad huh..
c) More than 100 frames or 25%(compared to K30) more battery life - always helpful if you forgot to bring an extra battery, or shooting many frames in a sports event and running out of battery juice fast. Psychologically, you only need to tell yourself that you have to stop shooting later into the event.
Other nice to haves:
d) Video filming: Autofocus throughout filming, focus peaking feature if you using manual lens for videography (K30 automatically disables this during videography losing a key focus aid), microphone jacks as you have pointed out... (but if you don't do video, then this is irrelevant)
e) Lighter (but not 30g only lar, so irrelevant)
f) Price is more than $100 cheaper... but of course, irrelevant if you have $
Ok, now to address K30's 'advantages':
a) Although the K30 is err.. 1mm shorter, 4mm narrower, and 9mm thinner.. not sure if that is going to make a big difference. What Kei is trying to say is, if you really mind the size, you should be going for mirrorless cams, not DSLRs. If you don't mind, then I really don't see the logic of being ngeow on 36mm[SUP]3[/SUP] of space, therefore... irrelevant...
b) OVF vs EVF - most non-Sony users here does not even seem to have used the A57's EVF before, some even acknowledging that EVF technology has narrowed the gap by a lot through the years. Is the A57's EVF lag that significant? nobody can prove anything, but from Rashkae's F1 pics above, I don't see what's so bad abt the EVF. And EVFs have certain advantages that OVF can never have, as mentioned already, like seeing actually what will be the end product on your photo, reviewing without taking eyes off the VF, etc. But well, it's still a personal thing, up to you to try and decide. If you decide that you are ok with both, then this advantage is .. irrelevant.
c) Smaller lens - see (a). If size is really an issue, then you shd not be comparing DSLRs, but looking at mirrorless models.
d) Image Quality - yep, pinholecamera's site is a pretty useful tool to compare, but I don't think the A57's image quality is trash. Go check it out and see if you can live with it. If it is that good already, I don't see how a few clearer pixels will make that much of a difference. But again, it is up to you whether this is important, or relevant to you.
e) Weather Sealing - Relevant if you need it, irrelevant if not. Good camera bag will help to protect your camera in bad weather, if you are not shooting w it.
f) legacy lens - already addressed by Kei. Sony have Minolta lens too, though I do admire the quality of the old Pentax lenses. And they have maintained the K-mount thru'out the years ! BUT again, is this important or relevant to your uses above?
oh well, the argument will go on and on... Pentax camera is certainly good stuff... but Sony is as good, if not better in certain aspects, and it is these aspects that you have to decide whether is relevant to you.
and yes, go try the camera. No amt of theory here beats the feeling of it in the hands, and testing it. Enjoy the shopping process !