Upgrade to CISCO ASA

I have CISCO PIX 515E with firewall version 6.3 and PDM version 3.0(1) at my two sites. We have site to site VPN. I want to upgrade those both sites to CISCO ASA. Below is my show vesion output. Could you please suggest me which ASA I should go for. And also , is there any specific features I will  require from the new ASA, typically IPSec VPN , SSL VPN any IPS requirements and so forth.
=============================================================================
Flash E28F128J3 @ 0x300, 16MB
BIOS Flash AM29F400B @ 0xfffd8000, 32KB

0: ethernet0: address is 0009.7cb4.09bc, irq 10
1: ethernet1: address is 0009.7cb4.09bd, irq 11
2: ethernet2: address is 0002.b3a0.0b18, irq 5
Licensed Features:
Failover:           Enabled
VPN-DES:            Enabled
VPN-3DES-AES:       Enabled
Maximum Interfaces: 6
Cut-through Proxy:  Enabled
Guards:             Enabled
URL-filtering:      Enabled
Inside Hosts:       Unlimited
Throughput:         Unlimited
IKE peers:          Unlimited

This PIX has an Unrestricted (UR) license.

Serial Number: 406171466 (0x1835af4a)
Running Activation Key: 0x9f1d99ad 0xb62bf1af 0x1c1d3a40 0x3af39389
Configuration last modified by enable_15 at 10:24:04.623 UTC Tue Nov 11 2008