Karkand and Mashtuur are the best maps for SV98.
If you want to level up faster, play Dragon Valley and use APC's. When you die choose to respawn at the base to take tank or APC. Keep doing it and you'll earn a lot of points.
But if you prefer to snipe only, chill out and have fun with sniping, play Karkand/Mashtuur.
Besides being good for sniping, on these maps you can earn 60-80 credits for winning. Mashtuur gives 80 credits for a win. This is important because you want to earn credits and to buy yourself better weapon in near future, M24 for example, which is 45K credits. Remember NOT to buy M14, it's not worth it, you'll throw away 17.5K credits. You will unlock M24 by reaching 14th level, AFAIK, you will be able to rent it and bang with it.
Also, play on Official EA servers because on those servers are mostly low level and inexperienced players so you won't get pawned by very experienced players on clan servers. This is important too, you won't have any chance with SV98 against very experienced players.