I've been playing ddrum electronic kits since 1992. I still own a ddrum AT module, a ddrum4 module, a ddrum3 pad set and a ddrum4 cymbal and hi-hat pad set. I have also used a TD-20 with the full Roland pad setup quite regularly so I think I might be able to offer you some insight.
I will firstly give my opinion of some modules and then give a list of questions you need to make sure you answer or you will quite possibly not be happy with your purchase.
In my opinion, Roland gear is generally over-rated and I feel most people who recommend them are either new to electronics or have not used any other electronic gear for an extended period of time. With that said, with the exception of the hi-hats, the ddrum3 and ddrum4 modules are still better at reproducing accurate drum sounds than the TD-12 and TD-20. Roland really has the hi-hat down and it is one of the areas ddrum lacks, as it only has 4 possible hi-hat sounds - closed, open, half-open and foot-chick. The other areas ddrum could improve at the number of inputs, amount of memory and sample dump speed.
The Yamaha DTXTREME IIS is quite a good unit and I believe the Roland TD-20 is only slightly better than the Yamaha, but I would choose the Yamaha given the choice between the two.
I also have an older Alesis D4 and that module was good value for the price. I believe the DM5 is much better than the D4, but I have never had an opportunity to play a DM5. If budget is your primary concern, look at the cheaper Yamaha kits or even the TD-6 (ick, i know -- contradiction). An Alesis DM5 would be a good choice for someone only wanting to trigger effects, kick and perhaps snare sounds.
--opinion over--
Ok, so when you are buying an e-kit you need to answer these questions:
- Does the module have enough inputs for my pads/triggers? You will need a minimum of 10 inputs in my opinion - kick, snare, rim, 3 toms, 3 cymbals, hi-hat.
- If I want to add pads/triggers in the future, does the unit have the capability?
- Am I happy with the sound quality? (not the salesman)
- Can I add in new sounds or my own custom samples? Can I save my own kit configurations? Is the interface easy to program?
- Can I connect the module to a computer and does it come with computer editing software?
- Can I hear the playback via headphones?
- How many outputs does the unit have? Can I split the drums and cymbals to different output? Can I assign an output for the snare and kick, independent of the toms and cymbals?
- How easy is it to set the pan? How easy is it to adjust the gain and threshold?
- Does the module have on-board effects? Do I care if it doesn't (such as you already own a decent effects unit)?
- Does the module have a click track? Again, do I care if it doesn't?
- Does the module have the ability to accept a sound source input so I can play along to music tracks? Again, do I care if it doesn't (such as you already have a mixer)?
- When I strike one pad hard, does it trigger sounds from other pads?
- When I strike two pads at the same time, can I hear both sounds being triggered? If you have a dual-zone pad, can you strike the rim and not hear the pad sound? And vice-versa?
- When I strike a pad softly and build up to loud hits, how good are they dynamics represented?
- When I play a press or buzz roll, does it sound like a snare drum or a 'machine gun'? How easy is it to adjust the threshold or gains on the trigger inputs to reduce this?
- If your concerned about the noise made when striking the pads, how loud is it when the pad is hit? Can I change the heads to mesh heads to further reduce the impact noise?
- What is the quality of the hardware and pads/triggers? Are the pads single or dual-zoned? Are the cymbal pads choke-able? Do the pads offer position sensing depending on where the pad is hit?
- And finally, does the kit fit into my budget? If not, if I really want this, how long will it take me to get this?
Regardless of which module and pads you choose, make sure you answer those questions honestly and you are happy with the answers. I hope this helps someone choosing their electronic drum setup.
Which electronic drums did I choose?
I am still using ddrum. The ddrumAT was my second e-drum system after I first dabbled with the Alesis D4. I now own and use a ddrum4 unit, which I use with ddrum3 cast precision pads and ddrum4 cymbal and hi-hat pads. I can't speak highly enough about the ddrum4, especially regarding the sound quality and reliability. I like to use the ddrum4 triggered with an accoustic kit live in a mix of about 60/40 with mics. Below is a photo of my ddrum4 pad kit which I practise on.
For those interested, here is a scan I made of the ddrumAT Manual in PDF format [approx. 4Mb]. You can also download the ddrum4SE Manual in PDF format [approx. 3Mb].
Recently, Clavia has sold off ddrum to Armadillo Enterprises in the USA. I am waiting to see what develops of this.
If you are interested in more information about the ddrum4, take a look at Armadillo's site or visit the ddrums.com forum.
Here are some pictures of my setup:


Favourite ddrum4 Sounds
In the days when the ddrums.com forums were alive, we often debated about our favourite sounds. These are still the sounds in my favourite 2 kit setups.
P01 - Rock Drum Kit
KICK_112 Heavykick4 dd3
SNRE_132 SON 14x10
RIM_134 Rim of 132 SON 14x10
TOM_304 DW 10Dipl.S&H.mid
TOM_305 DW 12Dipl.S&H.mid
TOM_307 DW 16Dipl.S&H.mid
CYMB_723 DCride1 DRY6S
CYMB_715 KAcrash3 3S (Pitch +3)
CYMB_715 KAcrash3 3S
HHAT_704 DChihat1 DRY7S
P02 - Pop/Dance Drum Kit
KICK_220 Record Kik 11
SNRE_248 Record Snr 3
RIM_200 MIX 5S
TOM_265 Drowned tom 1 (Pitch +6)
TOM_265 Drowned tom 1
TOM_266 Drowned tom 2
PERC_005 Cabasa
CYMB_021 Zild splash 10
CYMB_715 KAcrash3 3S (Pitch +4)
HHAT_200 ASRXHat9009
If you have these sounds for your ddrum4, give them a go!