I have a 7336SP. Just got it. I was in the same situation as you, used the search feature of this site, and discovered that the 7336SP and 7424 are exactly the same machine, with the EXCEPTION of the counterweight.
Technically, the 7336SP is made for 6 inch pads, and the 7336SP has a 6 inch counterweight. The 7424 has a 5 inch pad and a 5 inch counterweight.
So, if you took off the counterweights and pads, you'd have the same machine.
Which one should you get? The 7336SP at Lowe's is only $99 while the 7424 is usually around $125-$140 around car care places. It's up to you, but keep in mind that Pad kits on autopia-carcare.com and CMA (properautocare.com) include a 7424 with pads, backing plates, full packages. I've never seen a pad kit that includes a 7336SP. So you could get the 7336SP with for $100, then get the Sonus DAS Pad Kit (59.95 online at autopia-carcare.com) and your total would be about $159.99. If you got the 7424 kit from autopia-carcare.com, it would include a 7424, the Sonus DAS Pad Kit, for $179.99.
I chose the 7336SP because it was inexpensive and the same thing. Some say the 6 inch counterweight (7336SP) causes less vibration when used with a 5 inch pad, so here's a link with a comparison of Counterweights
Click Here
Good Luck with everything. I'll leave you with another great link on the different models.
Click Here
Carl