I have someone interested in buying my two RF t1500bdcp amps. Ill be running two xcon 15s d1 in 4 cubes per sub. Which amp is better and why between cresendo 3500d and sundown 3500v2? And for that matter would it be wise to go from what i have to what im looking at?

In my opinion it won't matter at all. Get the one that fits your budget the best.

I'd say Sundown, or keep what you have.

Thanks Duran, thats mostly my problem, they both come in less than what im selling my rf's for. Just curious if the 300  more bucks was worth the sundown name or not

How is your electrical system?

270 amp alt 1/0 wire diehard platinum under hood, small stinger agm in rear

I would never give up those Rockfords for either of the amps you want. 

Its settled then, ill keep my fosgates, they are quite beast

No reason to ditch them.  As Tirefryr mentioned I don't see either of the other two choices being any real improvement, other than the convenience of having 1 amp as opposed to two.

Thanks Impious I appreciate the advice

You can link those together I think. Buy the link cable and strap them together. Put a bigger battery in the back if you can fit it. Done deal.

I don't think they are linkable unless i have missed something. if so please correct me i would love to link them