I am thinking about getting a SD4. How's it doing for you, any major problems?

Out of the box, it was a bit frustating with ABS.  That was solved by moving up to glass on the bed & some hairspray for stick.
Now I am getting functional prints, but there are a few other problems.

Cons:
1. advertised bed area is not correct.  The print head / carriage will crash into various mounts and bolts before you get the whole 8x8x8 print area.  You get most of it, but definitely have to watch the left side corners.
2. Power supply is currently dying on me, or I should say the fan in the supply is dying on me.  This is with low hours of use.
3. Board pulls power from USB even when you unplug the power supply.  So the fans keep spinning, granted slowly.
4. no On/Off switch, no SD card features.

Plus:
1. Budget priced.
2. Extruder -alum- design is much improved over SD2
3. Lots of mods out there to improve the machine.

If you can live with making a few upgrades yourself, it's a decent printer.  If you want a great -out of the box- experience, then you may want to look at something else.

If all you want is fan control, the Printrboard supports it. 

On the other hand if you want more, than I would suggest either a RAMPS or a RUMBA.  Both are a a step above the basic Printrboard and offer dual-head, LCD, fan control, and SD options.  Plus they have better support for higher powered hot ends and heated beds.

While I could do the soldering to make the Printrboard fan control usable, I think I will go for another board.  I would like to untether the PC.  So LCD & SD card options sound like the way to go for me.

On the other hand if you want more, than I would suggest either a RAMPS or a RUMBA.  Both are a a step above the basic Printrboard and offer dual-head, LCD, fan control, and SD options.  Plus they have better support for higher powered hot ends and heated beds.

I have a Solidoodle 4 and would like to start some more serious upgrades beyond the glass bed that I have completed.

I would love to add fan control when I upgrade the hotend.  So that brings me to my question.

Should I upgrade the controllers?

If so, what's the best one out there to move up too?