Ok so i did some quick research to try and figure it out. And this is what i got:
1xRTT
1x (single-carrier) Radio Transmission Technology
The first in a family of cdma2000 1x digital wireless standards designed to extend and replace the IS-95 CDMA standard. 1xRTT is sometimes referred to as a "2.5G" standard.
Compared to the IS-95 CDMA technology it replaces, 1xRTT offers increased network voice capacity. This benefit requires support on both the base station (tower) and handset (phone). If everyone using a given tower has a 1xRTT phone, twice as many people can use that tower at the same time, compared to the old IS-95 standard.
1xRTT also offers much faster data speeds. The initial release - release 0 (zero) - supports data speeds peaking at 144 kbps. Typical real-world speeds are closer to 60-80 kbps.
A second release of 1xRTT was planned - release A - which doubled data rates at 288 kbps peak. Many carrier chose to skip 1xRTT release A, however, and move directly to 1xEV-DO.
1xEV-DO
(EV-DO)
Part of a family of CDMA2000 1x digital wireless standards. 1xEV-DO is a "3G" CDMA standard. EV-DO originally stood for "EVolution, Data-Only", but recently is also referred to as "EVolution, Data-Optimized".
EV-DO provides data rates over 10 times faster than 1xRTT, the previous data technology for CDMA networks.
Unlike other "1x" standards, EV-DO only addresses data - not voice. It requires a dedicated slice of spectrum, separate from voice networks using standards such as 1xRTT.
There are currently two main versions of 1xEV-DO: "Release 0" and "Revision A".
Release 0 is the original version, and the first to be widely deployed. Rel. 0 offers data rates up to 2.4 mbps, averaging 300-600 kbps in the real world. This is much faster than the 50-80 kbps typically offered by 1xRTT technology. Rel. 0 data rates are identical to 1xEV-DV Revision C.
Revision A integrates most of the faster data technology from 1xEV-DV Revision D, and improves latency. These enhancements allow features such as VoIP and video calling.
Although EV-DO does not include voice capability natively, Rev. A is fast enough to support VoIP technology at service levels equal or better to 1xRTT voice technology. This may be a future upgrade path for CDMA carriers if EV-DV development remains stalled.
In terms of data speed and general technology evolution, the closest equivalent to EVDO for GSM/WCDMA networks would be HSDPA.
1xEV-DO is based on a technology initially known as "HDR" (High Data Rate) or "HRPD" (High Rate Packet Data), developed by Qualcomm. The international standard is known as IS-856.
This information was found from :
1xRTT:
http://www.phonescoop.com/glossary/term.php?gid=150
EVDO:
http://www.phonescoop.com/glossary/term.php?gid=151
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So it looks like the difference is the transfer rate for data.
1xRTT: 288 kbps peak ~ real world 120-160kbps
EVDO: 2.4 mbps ~ real world 300-600 kbps
So as you can see there is a big speed difference. EVDO is also considered "3G".
Hope this helped