Most difficulties people have in using lead-free comes from one of three things:
1. a poor soldering iron
2. bad quality solder (the cheap stuff with bad flux is bad, duh)
3. poor technique (among other things, wipe your tip just before using, not before putting it away)
I like the Chipquik SAC305 with no-clean flux and other people I've recommended it to find it no harder to work with than Sn63Pb37.
If you are just starting out - and will therefore by definition have a poor iron, cheap solder, and poor technique - leaded is definitely the way to go. Once your first spool of leaded runs out, it is probably time to switch to lead-free.
When a joint is bad, you get obviously poor wetting and weird mushroom shapes, but even so a newbie will not really notice that even using leaded solder.
If you are starting out, and you have a poor iron, cheap solder, and poor technique, you have already made two grave mistakes. We always urge people starting out to shell out in the $50 range for something that won't actively make them suffer, and they do just fine with SAC305.
The cloudy diffuse look of lead-free SAC305 is more distinctive to my eye.
When I take production (lead-free) hardware off the line for dev work, the first step to removing a large part is to flood it with leaded solder to reduce the melting point.
Has there ever been an occupational study of lead levels among hardware engineers? I'd be interested to see it.
Took some effort with rollers to be able to pan/rotate the board while it's on the heater but does make lead-free feel like leaded for me (on dense but relatively small boards anyway.)