Uhm not entirely sure what you mean by better but here's an overview from what I understand. keep in mind I am still new to watches.

St16 is based off a Miyota 8200 but with a Seiko autowinding mechanism.
This is an example of a Miyota 8200 series (3 hands time/date 8205):
http://www.citizen.co.jp/miyota_mvt/download/pdf/parts_8205_8215.pdf

The ST25 seems to be a clean sheet design for openheart according to Chascomm

No, it's a clean-sheet design specifically for the open-heart balance at 6 o'clock layout. It just happens that is is made to a much higher standard than the majority of open-heart movements made by other companies (I don't count any Swiss, Japanese or Russian open-hearts because they are not true open-heart designs).

Some more info by dkbs

ST-25 is more like an enlarged clone of Rolex movement (exclude auto bridge) with in-house auto bridge on top and 77xx style date mechanism on the bottom. It is very stable and accurate movement (can stay on less than 2 second/day for several months if adjusted properally) but I don't know the durability.

Why it's better I am not sure, all I know is that it was designed specifically for an open heart balance, using double bridged. I am waiting on my large watch wrench so I can pry open this sucker.

 

it's also a 28800 bph movement as oppose to the 21600 bph movement found in the st16. that alone means it can be regulated to a higher degree of accuracy. It also has a quickset date pusher as oppose to just a quickset date on the first crown position. The date changes instantly rather than over a period of hours on the st16. It has a full bearing rotor rather than just a jewel cap, and if you ever get a chance to open one up, the movement is BEAUTIFULLY decorated and finished, with all beveled edges. I'm sure there are other upgrades in terms of material, shock protection, etc... but I would put the ST25 as an eta2824 equivalent. There is also the provision for moonphase and big date complications and a directly driven second hand, taking away any stutter that would commonly be seen on the st16 movement.

 

Thanks for the info. So the ST25 date is on the bottom rather than the ST16's right hand side?

Edit : As for the instant change date...does that mean theres no danger of changing the date between 12 and 3 am?

 

This is all based on my experience with ONE ST25 watch, but yes, the date 'snaps' from one number to another over a period of seconds, so there wouldn't be a danger of changing the date between 10 and 2. For the one I had, the date was located at the 3 o'clock position, but I've seen them at the 6 and big date at the 12 before.

 

Are you sure about the BPH? I have most anecdotal sources saying 21,600 BPH for the ST25.

 

I just bought a ST25 off trusthonestman and I amazed at the accuracy. Four days on a watch-winder and it is spot on. I have also bought a ST16 off him and he has promised me an accurate movement for the cheap watch, can't wait to test it. I also have a ST21 and a ST18. The ST21 is a few seconds out. The ST18, surprisingly, is the most disappointing at being 20s out. I'll have to measure it on my wrist to see whether it has a problem with watchwinders.

 

I found a great article on another site that talks about the difference of BPH and how it can improve a watch, and wanted to share it.

Apparently one of the main advantages is shock resistance. Ye olde style (not really since faster BPH is a more modern concept).
Does Faster Mean More Accurate? - TimeZone