What kind of collars are you looking for? GPS, Argos, VHF, or just marking collars? The answer might well depend on that, as Ushma pointed out. Large deer such as Swamp and Axis deer can be fitted with almost any kind of collar you might think off, but smaller deer, such as hog deer, would have limitations on the size and weight they can carry on. The "rule of thumb" is that a collar should never be heavier than 5% of the deer's body weight (BW). But be careful with this rule. For brocket deer in Mexico (12-15 kg) we started using collars that were about 4 or 5% of their BW and they were way to heavy for them. We later changed for a smaller Telonics model that was about 2% their BW.

I am looking for GPS collar and want to follow the animals for 1 year

If you give us a bit more information we can suggest a cost efficient solution. What are the objectvies of your study? How many collars (You may not need a collar. A tag which is much cheaper might do.) would you like to deploy? How big an area do you think you will need to monitor? Do you already have any telemetry equipment? What type of habitat will the animals be in (we can guess from the species you mentioned but better information will influence the best solution)? Are the areas that the animals will inhabit during the study be accessible to the researchers?

I want to study the ranging behaviour of swamp deer and other sympatic ungulate (hog deer and spotted deer). About 10 swamp deer, 5 spotted deer and 5 hog deer is planned to collar. The area is grassland and shorea forest and ofcourse the researcher can access the area easily except during monsoon season when the grass is tall but can access with difficulty.

You do not say whether you are looking at movements within a day or over longer periods of time. If the former, since you are planning to tag a relatively small number of animals and the area is relatively easy to access, I would consider using GPS tags that will give easy to interpret information on detailed movements. However, GPS do not work under heavy canopy cover and so you will have gaps in your data if the deer move to heavy canopy cover.

Radio tags are much cheaper, and if you do not need detailed location information, they can provide less detailed but more reliable data. They work well in heavy forested areas and areas with heavy canopy where GPS will not work. Setting up the antennas and mapping the detection field to recreate deer movements will take a few weeks of work so it depends whether you want to spend your money on personnel time or the tags and retrieving the data. The stations to monitor the tags, once they are set up, can go weeks or more without downloading the data so you recover some of your up front time over the period of the project. To go this route you will want receivers with antenna switching and set up adjacent receivers so that tags will be detected on at least one antenna on adjacent receivers. Purchase your tags with detection distance in mind because detection range depends on the power output of the tag. The pulse interval for terrestrial situations like this can be programed to be long so that the tags will last a long time even with high power output. If tags are coded, you can minimize the number of different fequencies to be monitored and 20 tags on one frequency is well below the capabilities of good systems.