[aixguy]

In a nut shell:
Bottom feed:
Holds lots of paint in a jar or metal cup
Requires a jar for every color if you don't want to open it up and wash out the paint that was not used. Jar cost money.
Requires higher airflow and pressure to suck the paint out of the jar.
Usually has a larger nozzle and needle to let the thicker paint that textile artist use flow better. This reduces the detail you can get out of the brush, especialy as a begginer.
More and slightly harder to clean.
usually less expensive.

Gravity feed:
Holds small amount of paint
Requires less paint since you can put as little as 1 drop of paint in the brush and spray it.
Requires less air flow to make the paint spary since gravity helps move the paint and it does not need to be sucked UP the tube from the jar.
Usually has a smaller nozzle and will allow for smaller detail
Easy to clean, no jars and tubes to deal with.
can be slightly more expensive but there are no jars to buy.

Personal experiance:
I bought a bottom feed, (vl) then a dozzen metal cups at $4.99 each.
Next bought an anthem 155 since it could use the same cups and I thought it would be better for me since I have small hands and the VL is fat and uncomfy to hold.
Next I wanted more detail and bought an Iwata HP BH.
Next I wanted a gravity feed brush to give wider coverage like the bottom feeds, so I got a Eclipse CS.

I also started this adventure wanting to paint Haloween props.. found out I could do other stuff to. Knowing what I do now, I would have gone with a gravity feed bursh like the Iwata HP-C+ or Richpen 113C or the Eclipes CS and skiped the bottom feeds all together, but that is just me.

Good luck!