If you are using Sonar with a laptop what audio interface are you using and how well is it performing on your laptop?

There are plenty of USB2 audio interfaces that work well with laptops.
What type of I/O do you need?
Will you be monitoring thru software in realtime (in which case you need lowest possible round-trip latency)?

Yes , that right, it would depend on what you will be doing. I use my netbook or an old P4 Laptop at gigs for music playback and either use the on board or this funky Behringer interface which is about as bad as they get for performance. But it is all you need for that. 
If your going to work with Sonar then I would use one like my Scarlett 6i6 which performs well and is very portable. 
If your going to run Guitar rig or heavy use VST's then your going to want a top of the line interface with low RTL as Jim say's. 

Also, if its a new laptop make sure it has a true USB 2.0 port, or a USB interface may not work well with it.

I have a laptop and everything is fantastic with Sonar, even with 120+ tracks and lots of busses.

I think Focusrite audio interfaces are strong. I have 2 Scarletts.

But what gets me excited when mentioning audio interfaces is the KB-37. That's my mainstay for guitar and vocals recording with no latency issues. I use Amplitube (not PodFarm) with it and I can input dry guitar to a track and hear it fully loaded with effects while playing it with no latency. Same for vocals with a mic. And that's just the starting point of good things to say about it. It just works.

In sum, I have Focusrites and really like them. I use the KB-37 as my mainstay.

A couple of clips on it:
https://www.youtube.com/watch?v=zwBR1OfHRtM

https://www.youtube.com/watch?v=cRpCXWSC8TE

P.S. I'm a laptop Sonar user. Since I switched to a laptop I can't imagine ever going back to a desktop.

My goal is to be able to record vocals and instruments and then dump that into my main computer

I have the old Motu MK3 ultralite and it works great so I bought the hybrid so that I can be mobile and I have been extremely dissapointed with. For whatever reason the audio is defaulting to SPDIF outputs. I taking it back and looking for something else. I want to be able to record quality vocals on the level of the Motu MK3 and be mobile. I am still thinking of buying a better laptop for this so any spec reccomendation.

Jim Roseberry
There are plenty of USB2 audio interfaces that work well with laptops.
What type of I/O do you need?
Will you be monitoring thru software in realtime (in which case you need lowest possible round-trip latency)?

Windows and USB I think firewire connections are better but that would mean buying a laptop that have a firewire connections. There is a possiblity I could use the same interface for live gigs

I have the ultralite for my laptop and the 828 for my desktop..
 
The only way that spdif is set as the default main output for the computer is if you set this up in your control panel/sounds/playback to be the default mains out device...its not an ultralite issue per se.
 
Other than that, the only flaw with these interfaces is that you cannot use the computer mains audio output as an input to one of the 8 output bus, and the one easy way to overcome this is to have mains out set to spdif and use a short cable to connect spdif out>spdif in.
 

BMOG
I have the old Motu MK3 ultralite and it works great so I bought the hybrid so that I can be mobile and I have been extremely dissapointed with. For whatever reason the audio is defaulting to SPDIF outputs. I taking it back and looking for something else. I want to be able to record quality vocals on the level of the Motu MK3 and be mobile. I am still thinking of buying a better laptop for this so any spec reccomendation.

Mystic38
I have the ultralite for my laptop and the 828 for my desktop..
 
The only way that spdif is set as the default main output for the computer is if you set this up in your control panel/sounds/playback to be the default mains out device...its not an ultralite issue per se.
 
Other than that, the only flaw with these interfaces is that you cannot use the computer mains audio output as an input to one of the 8 output bus, and the one easy way to overcome this is to have mains out set to spdif and use a short cable to connect spdif out>spdif in.
 

BMOG
I have the old Motu MK3 ultralite and it works great so I bought the hybrid so that I can be mobile and I have been extremely dissapointed with. For whatever reason the audio is defaulting to SPDIF outputs. I taking it back and looking for something else. I want to be able to record quality vocals on the level of the Motu MK3 and be mobile. I am still thinking of buying a better laptop for this so any spec reccomendation.

I ended up getting a new unit and things seem to be working properly.  What I believed happen is I was told by Motu support that I could install both devices the Old MK3 and the Hybrid on the same computer.  After doing that is when the audio started defaulting to Spdif. Going back to Motu support they told windows can't handle both devices on one workstation, so I believe the drivers got all out of wack.  To fix my old MK3 I had to restore my computer back to a restore point before installing the Hybrid.  Now I only use the Hybrid for my Laptop and I am not having any issues