I have an ageing UA25 which works well but is USB 1 and with Windows 7 there is a known issue where a USB 1 device attached to a USB2 port causes periodic CPU spikes. Nonetheless things work fairly well on my core i7 laptop but I'm thinking about replacing it anyway.
 
I've heard good things about the RME Babyface but this is rather more than I need and is not cheap - can anyone recommend a unit which ideally is
(a) externally powered and NOT buss-powered - ground loops with USB powered audio interfaces have been the bane of my life.
(b) Has 2 analogue in and 2 analogue out with balanced I/O for both (more outs could be useful but not essential)
(c) Has really good low-latency performance for realtime playing of softsynths.
 
I looked at the Focusrite Scarlett models but there is some question over the latency. Not sure about Roland's newer units; their new large device, can't remember the name,got slated by Sound on Sound for the worst latency they'd ever measured, which doesn't exactly fill me with confidence. Any recommendations or do I just go for the RME?. I don't much like breakout cables, though, I'd prefer everything on the box.
 

Many factors determine round-trip latency, of which the interface's contribution (typically ~1ms) is relatively minor. Optimizing Windows is vastly more significant than the choice of audio interface for achieving low latency.
 
So choose your new interface based on features and reputation. Don't pay $1,000 or more for a high-ish end device on the assumption that it will be more efficient. RME is a highly-respected vendor, but so are Lynx, Echo and MOTU. Look into lower-priced units from Roland and even Behringer. But base your decision on features first. 
 
Two inputs and two outputs may be all you need, but you might be surprised how useful additional I/O can be once you have it. Four or more outputs means you can have a separate headphone mix, or hook up another pair of speakers as an alternate reference. Having 8 inputs means you can keep multiple devices plugged in all the time without needing to swap cables or use a mixer. You can have others over for collaborative jams and record everybody together. Or record a drum kit. Having S/PDIF capability could come in handy, too (your UA-25 has it, but you probably don't use it because it's optical) if you ever use an outboard synthesizer.

I'm really raving on my recently acquired Motu Ultralite Mk III Hybrid. It's a little less expensive than the RME - has two pre's +  6 additional line-ins, 10 bal outs plus phones. Nice rugged metal case, not bus powered with USB, can do Firewire also. Built-in mixer & effects for tracking. Does ASIO, WaveRT..
 
For the amount of features it provides, it's really a good value at it's price point!

There are so many choices out there. It's amazing and a maze all at the same time. I recently completed a "take my time" approach to upgrading from a delta 1010 card to a tc impact twin. Which btw, I could recommend the delta 1010 as a great card for the ebay price you can get one now (usually around $120 or so). However, I'm not looking back from the first time recording through the impact twin. Very nice card.
 
The PC interface products I've heard the best recommendations for come from these companies:
 
RME - TC Electronics - MOTU - Roland - Echo - Steinberg - Presonus - Focusrite - M-Audio Profire - Native Instruments 
 
As I sorted through these I ruled out the ones you couldn't bypass the internal preamps. I was also highly interested in conversion, low latency and liked the perk of onboard dsp.
 
Of all of the articles I read from forum posts to sos reviews - I found this one a very telling review. The author is reviewing a Focusrite Forte, however within the article are tests results from comparisons to multiple interfaces.
 
Interface Review
 
 
 
All the best!

no digital in and out nixes the Forte for me.
 

@batsbrew: I was really pointing out the interface comparison results vs recommending the forte.

i gotcha...
 
but i was seriously looking at the forte, because of all it's good qualities.
but alas, no digi IN/out

musicroom
As I sorted through these I ruled out the ones you couldn't bypass the internal preamps.

Why is that?
 
Assuming you are referring to line inputs, do you actually have any direct knowledge or evidence of non-bypassable onboard preamps causing any problem?
 
Are you aware that even very high-end A-D converters employ preamps on their line inputs for buffering the input signals before they are applied to the converters?

Goddard

musicroom
As I sorted through these I ruled out the ones you couldn't bypass the internal preamps.

Why is that?
 
Assuming you are referring to line inputs, do you actually have any direct knowledge or evidence of non-bypassable onboard preamps causing any problem?
 
Are you aware that even very high-end A-D converters employ preamps on their line inputs for buffering the input signals before they are applied to the converters?

 
I tend to think that less gain staging areas in my signal chain is a good thing. And yes, I have ran my outboard pre thru a decent onboard pre before and found the sound to be slightly affected in a negative way. I have never had the opportunity to do this through a high-end converter though. I'm not doubting you for specific interfaces. Of course each manf will tell us what we want to hear in regards to the onboard pre not affecting the outboard pre's signal to converter. For a test, I think I will run my outboard pre through my new impact twin's pres and report back. However, I'm very happy I have the option with this interface to bypass the pre and send signal directly to the converters. To me, it's a failing when manufacturers don't offer this routing option as a SOP. 

A/D's will have likely have buffer circuit on their line-in's for isolation, but I wouldn't call it a pre-amp.