Petary, I'm on the same page as UncleToad. Each type of bass has its own
unique sound and it's either what you like or not. As much as I love my KYDD Carry-On 4 EUB (
www.kyddbass.com), it's not a double bass. Even the maker, Bruce Kaminsky, says the sound "is very similar to an amplified (not mic'd) acoustic bass." If you're really looking for a double bass, get a double bass. Even a cheapie will give a more acoustic sound than an EUB.
Now, personally, for what I play, my EUB is perfect. Many years ago, I took double bass lessons and, between my lack of formal music training and an impatient instructor, I soured on the instrument quickly. I went back to my MusicMan Stingray and didn't look back. In 1999, I saw Al Tharp of the cajun band Beausoliel playing an EUB (a KYDD, in fact). It was a mix between a fretless electric and an upright. Way cool. I bought one and loved it ever since.
The best way I can explain it is to say it's a fretless electric bass played with an upright technique. I know I solo very differently on my EUB than on my fretless Warwick Thumb. The sound is very different than an electric, but it's not an upright - it's a hybrid. Most other band members will swear that it sounds exactly like an upright, but bassists won't (what do most guitarists know from bass anyway?

).
One other piece of advice I can offer was mentioned earlier: get the best amplification system you can. A "run of the mill" bass amp will only frustrate you. The base sound that comes out of an EUB is significantly different than an electric bass and the eq controls have their base frequencies in the wrong place. Some type of parametric eq for the mids is a good start, but go for an amp that does not color the sound of the instrument. Personally, I bit the bullet and went for an Eden 550/212 combination. It works well for me and gives me a sound like no other amp/cab combination I've tried. I would look at an Eden Metro, maybe an Aguilar, an Epifani, Phil Jones, etc.
Another important issue is a good preamp. Unless the EUB has a built-in preamp that matches the impedence of a piezo-based pickup system to a "regular" amplifier. For a much more thorough discussion of impedence matching, refer to Bob Gollihur's website.
Bottom line, if you're looking to get an upright sound on the cheap, an EUB ain't gonna do it. Between the base cost of a good quality instrument ($1,500+), a good preamp ($80+) and a good amp system ($1,000+) It would be better to get a mid-range upright bass, good strings and an awesome mic/pickup system. However, if you like the concept of a fretless electric sound mixed with a little upright played with an upright technique (including bowing), an EUB is THE BOMB. Another cool thing is bowing while going through effects. Flanging, delay, chorus, envelope followers, all add a coolness for the right project. I play with a few "experimental" musicians and the EUB adds the right type of mojo for that.
Plus, they just look freakin' cool on stage...
Coop