SV650 will be a great starter.
Here are the reasons. The SV is a twin, in a milder state of tune then the 4cyl inline supersports....
The general explanation goes somewhat like this... If you look at any bike stats you'll see HP and Torque. Assuming the Torque was the same, if it is at higher rpm, the engine will develop more power. If its at lower rpm, the engine will be more friendly, with a better low end. The point at which peak torque hits is controlled (mostly) with cam profiles.
Now, twins cannot spin as fast as inlines. Its because their pistons are heavier, and create more vibration when they change direction. For this reason, most twin engines are tuned to produce their power down low, also there are exceptions (Look at ducati supersport.
An Race-rep inline 4 (600cc) will produce virtually no power untill 6k rpm. Its real easy to stall... it produces some power between 6-10krpm, and around 10k they start making lots and lots of power. An SV650 on the other hand will start with decent power at around 2k. This power will climb very predictably with the rpm, untill it hits red line at around 9-12k (dont remember). So it makes less power, but in a more predictable fassion, without the suprisingly peaky nature of inline 600.
Another thing to look at is rake, trail, and wheelbase numbers. These in combination define the stability and manuverability of a bike. Really short trail, small rake, and short wheelbase bikes will be twitchy, responding very quickly to every input (wether its a correct or a mistaken one), and will have a lesser tendancy to try to come back up after being leaned. More rake, trail and wheelbase, will make the bike more stable, more forgiving to accidental inputs, and the bike will have more of a tendancy to stand back up after a lean, but it will require more effort to make it turn.
Hope that helps.